South Korea and US begin military drills Anti-war activists stage a protest against a joint military exercise between South Korea and the US near the US embassy in Seoul on Monday South Korea and US forces have launched an 11-day land and sea exercise, in the face of North Korean protests that such "sabre-rattling" could lead to military confrontation. Exercise Key Resolve, the second phase of the allies" annual war games, went ahead as planned on Monday and will involve 13,500 troops. The war games have sparked angry rhetoric from Pyongyang, which also condemned new UN sanctions imposed in response to its recent rocket launch and nuclear device test. "It is the US imperialists" trite method of aggression to tighten sanctions and escalate the moves to stifle [North Korea] militarily," state media said on Sunday. On Monday, North Korea ceased responding to routine checks on a hotline used for communication with South Korean officials, Seoul said. This is the first time it has done so since the hotline was revived in January 2011, and follows a similar breach of routine communication with US forces last week. Tensions have risen as North Korea responded angrily to last week's new UN sanctions against it, which require states to inspect any suspicious cargo heading to or from the country. Pyongyang has pronounced itself ready for a "second Korean war" - a longstanding theme in its propaganda. "North Korea routinely issues threatening rhetoric against the South and the US whenever there are military drills or UN Security Council sanctions," said Lee Woo-young, a professor at Seoul's University of North Korean Studies. However, the sheer volume of belligerent statements from the North has put Seoul on alert, a South Korean official said. "Although in terms of content it's not new, these announcements are coming in a back-to-back series, and in the aftermath of a third nuclear test, and before and after the UN Security Council's latest resolution," the official said. So all this combined has created a greater concern for security in the South. Of particular concern will be North Korea's invocation of its 2010 shelling of Yeonpyeong, a South Korean island, which killed two soldiers and two civilians. This was carried out to punish Seoul for its "shelling [of waters claimed by North Korea], seized with war fever," North Korea said on Sunday, questioning whether Seoul had forgotten the incident. State media also said that Kim Jong-eun, North Korea's leader, had visited an artillery unit that took part in the 2010 shelling, urging it to "deal deadly counterblows at the enemy if a single shell is fired on the waters." Seoul's defence ministry said that its exercise was "not an offensive drill" but that South Korean forces were ready to "punish" any provocation by Pyongyang. North Korea is believed to be conducting a military exercise of its own, it added, without providing further details.