Seoul, South Korea (CNN) North Korea is believed to be moving an intercontinental ballistic missile (ICBM), a South Korean lawmaker said after being briefed by the country's intelligence service. 
 
 The lawmaker told CNN Tuesday it was unclear when the movement was detected, what the direction of the projectile was and how it was being transported. He attended the briefing by South Korea's National Intelligence Service (NIS) in Seoul on Monday. 
 
 All eyes have been on North Korea following the country's sixth test of a nuclear weapon Sunday. Seismological data indicated the weapon was the most powerful ever detonated by the rogue nation, nuclear experts said. 
 
 North Korean state media claimed it detonated a hydrogen bomb, also known as a thermonuclear weapon, which could be fitted atop a long-range missile capable of striking the United States. 
 
 Weapons experts say it's almost impossible to verify if the warhead and missile could be successfully paired unless North Korea were to actually fire a nuclear-tipped ICBM. 
 
 The country has test-fired a number of missiles this summer, including two long-range ones in July and an intermediate-range one in August that overflew the Japanese island of Hokkaido. 
 
 Lawmaker Kim Byung-kee told reporters Monday after the same briefing that the NIS said North Korea may test-fire an ICBM towards the North Pacific at a lower angle than the two tests in July, which were lofted, meaning they flew higher but not as far. 
 
 Live-fire drills 
 
 The South Korean Navy announced Tuesday it conducted live-fire drills off the east coast of the Korean Peninsula to check its "immediate operational readiness" after the country's Air Force and Army conducted their own joint drills. 
 
 South Korea's Navy conducted a live-fire drill in the waters off the east coast of the Korean Peninsula in response to North Korea's Sunday nuclear test. 
 
 "Wherever it is, whether on or under water, if North Korea provokes, we will immediately destroy and bury them at sea," the Navy said in a statement. 
 
 While South Korean forces have flexed their muscles, diplomats in New York gathered at the United Nations and condemned the nuclear test. 
 
 Nikki Haley, the American ambassador to the United Nations, said Monday the United States would circulate a resolution in response after urging her colleagues to adopt the strongest sanctions measures possible to stop Pyongyang's nuclear program. 
 
 "Enough is enough," Haley said. "North Korea has basically slapped everyone in the face in the international community that has asked them to stop." 
 
 Another lawmaker who attended the Monday briefing, Lee Cheol-woo, told reporters the NIS informed them that Pyongyang had dug extra tunnels at the nuclear test site and could explode another one "anytime." 
 
 Rift? 
 
 South Korean President Moon Jae-in and his American counterpart, President Donald Trump, spoke by phone Monday and agreed to lift current restrictions on the payload weight of South Korea's ballistic missiles, according to a South Korean presidential spokesman. 
 
 But signs of a rift between the two leaders have become apparent despite the decades-long alliance between Seoul and Washington. 
 
 Their phone call came a day after the nuclear test and followed a tweet from Trump in which he criticized South Korea for "appeasement" when it comes to dealing with its northern neighbor. 
 
 Moon has long been a proponent of more dialogue and diplomacy with North Korea, whereas Trump has said recently that "talking is not the answer." 
 
 "This is not the time for these two countries to be showing these cracks. North Korea is going to exploit that," said Jean Lee, a North Korea expert and global fellow at the Wilson Center. 
 
 Trump spoke twice with Japanese Prime Minister Shinzo Abe over the weekend, once before the nuclear test and once after. 
 
 Diplomacy 
 
 Moon and Abe are both traveling to the eastern Russian city of Vladivostok for an economic summit taking place Wednesday and Thursday. 
 
 They will be joined by Russian President Vladimir Putin, who is currently in China for a summit of the BRICS nations -- Brazil, Russia, India, China and South Africa. He reiterated calls for North Korea to stop nuclear tests but said dialogue needs to be the answer. 
 
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 "Russia condemns these exercises from North Korea. We think these exercises are provoking in nature but we should not forget and North Koreans should not forget what happened in Iraq," he said. 
 
 "Sanctions of any kind are usefulness and ineffective ... they will eat grass but they will not turn away from the path that will provide for their security," Putin said, referring to accusations that Pyongyang spends too much on weapons programs while its citizens starve. ||||| SEOUL/TOKYO (Reuters) - Detonating a nuclear-tipped missile over the Pacific Ocean would be a logical final step by North Korea to prove the success of its weapons program but would be extremely provocative and carry huge risks, arms control experts said on Friday. 
 
 FILE PHOTO: North Korean leader Kim Jong Un watches the launch of a Hwasong-12 missile in this undated photo released by North Korea's Korean Central News Agency (KCNA) on September 16, 2017. KCNA via REUTERS 
 
 North Korean Foreign Minister Ri Yong Ho suggested leader Kim Jong Un was considering testing “an unprecedented scale hydrogen bomb” over the Pacific in response to U.S. President Donald Trump’s threat at the United Nations to “totally destroy” the country. 
 
 “It may mean North Korea will fire a warhead-tipped (intermediate range) Hwasong-12 or Hwasong-14 intercontinental ballistic missile and blow it up a few hundred kilometers above the Pacific Ocean,” said Yang Uk, a senior researcher at the Korea Defence and Security Forum in Seoul. 
 
 “They may be bluffing, but there is a need for them to test their combined missile-bomb capability. They could have already prepared the plan and are now trying to use Trump’s remarks as an excuse to make it happen,” said Yang. 
 
 Such an atmospheric test would be the first globally since China detonated a device in 1980, according to the International Atomic Energy Agency. 
 
 Tests of nuclear-tipped ballistic missiles are rarer still. The United States’ only test of an operational ballistic missile with a live warhead was fired from submarine far out in the Pacific Ocean in 1962. 
 
 China was widely condemned for a similar test with a missile that exploded over its Lop Nur test site in the country’s west in 1966. 
 
 North Korea’s six nuclear tests to date have all been underground, the most recent earlier this month by far its largest. 
 
 “We have to assume they *could* do it, but it is exceedingly provocative,” said Vipin Narang, an associate professor of political science at Massachusetts Institute of Technology. 
 
 “To put a live nuclear warhead on a missile that’s only been tested a handful of times, overflying potentially populated centers. If it...doesn’t go exactly as planned....it could be a world changing event.” 
 
 North Korea has fired two ballistic missiles over Japan’s north Hokkaido region in the past month as part of a series of tests that experts say have illustrated unexpectedly rapid advances. 
 
 “They said Pacific Ocean, which pretty much means firing a missile over Japan,” said Melissa Hanham, a senior research associate at the U.S.-based Middlebury Institute of International Studies at Monterey, California. “They want to shut us all up for doubting they could build it.” 
 
 SERIOUS FALLOUT 
 
 While a missile would be the most ideal means of delivery, it is also possible to put a bomb on a ship and detonate on the surface of the ocean or in the sea, the experts said. 
 
 Either way, the radioactive fallout could be significant, as well as the diplomatic backlash from around the world. North Korea’s recent missile launches over Japan especially drew stern rebukes from Tokyo and the international community. 
 
 Japan’s Chief Cabinet Secretary Yoshihide Suga called Pyongyang’s remarks and behavior “completely unacceptable”. 
 
 Narang said a test high enough over the ocean would limit the radioactive fallout but risks included damage from an electro-magnetic pulse, something Pyongyang has hinted it might employ on an attack on the United States or its allies. 
 
 “If it doesn’t go exactly as planned and the detonation occurs at a lower altitude we could see some EMP-like effects for anything in the area. A lot of dead fish too.” 
 
 Pyongyang has launched dozens of missiles this year as it spurs a program aimed at mastering a nuclear-tipped missile that can strike the United States, in addition to its Sept 3 nuclear test. 
 
 If Kim’s threat materializes, it will be a “tipping point” for China, and may prompt many other countries to demand an “end to the regime,” said David Albright, founder of the non-profit Institute for Science and International Security in Washington. 
 
 “No one has tested above ground for decades and the radioactive fallout could be terrifying to many,” Albright said. 
 
 Other experts said such an atmospheric nuclear test is unlikely for now due to its substantial technical and diplomatic risks. 
 
 Joshua Pollack, editor of the Washington-based Nonproliferation Review, said it would be an “end-to-end demo of everything.” 
 
 “But I would be surprised if this were their very next move. They have yet to test an ICBM at full range into the Pacific,” said Pollack. “That will probably come first.”
– Following North Korea's most powerful weapons test yet on Sunday, a South Korean lawmaker tells CNN his country's intelligence service believes the North has an intercontinental ballistic missile (ICBM) on the move. Things get pretty vague beyond that: He didn't know the method of transport or when the movement was noticed. But Reuters does pick up some alleged details on those fronts, via an unnamed source quoted by South Korea’s Asia Business Daily. Its source says the ICBM started moving Monday, is only being moved at night, and is headed toward the nation's west coast. Reuters notes there's some likelihood that another test could come on or around Saturday: Sept. 9 is the country's founding day holiday. CNBC notes North Korea conducted a nuke test on Sept. 9, 2016. Two more details that allegedly came from the South's National Intelligence Service briefing: word that additional tunnels have been dug out at the North's nuclear test site that would facilitate future detonations, and suspicions that the next ICBM test firing might be directed toward the North Pacific but aimed at a lower angle, which would in theory allow it to fly further than previous tests, which had more of an upward trajectory. Meanwhile, the White House tells Reuters it has given "in-principle approval" to a request by South Korean President Moon Jae-in to abolish a limit regarding warhead weights, a move that would strengthen the power with which it could attack the North, if necessary. Meanwhile, Vladimir Putin on Tuesday gave his take on the situation: North Korea "will eat grass but will not give up the (nuclear) program if they don't feel safe."