U.N. nuclear watchdog agency in Iran for more talks The U.N. agency says Iran needs to clarify the "possible military dimensions" of its nuclear program Iran maintains it is enriching uranium to fuel civilian power plants Israel has made clear it considers a nuclear-armed Iran a threat to its existence (CNN) -- Officials with the U.N. nuclear watchdog agency begin a second round of talks Monday with Iranian officials over the country's nuclear program, a day after Tehran cut off crude exports to British and French companies in retaliation for a new round of sanctions imposed on the regime. The two days of talks come amid heightened tensions in the region, with Israel making clear it is pondering an attack on Tehran's nuclear infrastructure, while Iran warned it could cut off the narrow strait through which oil tankers sail in and out of the gulf. The scheduled talks between the International Atomic Energy Agency and Iranian officials are billed as an opportunity for the watchdog agency to clarify the "possible military dimensions to Iran's nuclear program," the group said. Iran says it is producing enriched uranium to fuel civilian power plants and has refused international demands to halt its production. But the IAEA reported in November that it had information to suggest Iran had carried out some weapons-related research. U.N. Secretary-General Ban Ki-moon said it is up to Iran to disprove the allegation. The Agency is committed to intensifying dialogue. It remains essential to make progress on substantive issues," IAEA Director General Yukiya Amano said in statement following the first round of talks in January. The talks in Tehran follow an announcement Sunday by Iran's oil ministry that it was halting crude exports to French and British companies, an order that followed a threat that Iran would cut oil exports to some European Union countries in retaliation for sanctions put in place last month by the EU and the United States. Iran has no difficulty in selling and exporting its crude oil. ... We have our own customers and have designated alternatives for our oil sales. We shall sell to new customers, who will replace French and UK companies," ministry spokesman Ali Reza Nikzad-Rahbar said in a statement. Israeli Defense Minister Ehud Barak has called for still-tougher sanction, saying that accelerating the pace of sanctions would force Tehran to return to nuclear talks. Meanwhile, Israel has made that it considers a nuclear-armed Iran an existential threat, and has made clear it is considering an attack on Tehran's nuclear infrastructure. The United States believes talk of military strikes against Iran's nuclear program is "premature" and has advised Israel that an attack would be counterproductive, Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, said Sunday on CNN's "Fareed Zakaria GPS." Dempsey said U.S. officials aren't convinced Iran has decided to pursue nuclear weapons. Meanwhile, economic and diplomatic sanctions appear to be taking a toll on the Islamic republic, he said. Tensions between Iran and Israel have been further heightened in recent days with two Iranian warships sailing through Egypt's Suez Canal into the Mediterranean Sea. It's only the second time such ships have crossed through the Suez Canal since Iran's 1979 revolution. "As the Navy affected the region with its presence in the Mediterranean Sea last year, the Navy's 18th fleet will in the best way carry the message of peace and friendship to regional countries, and display the might of the country and the sacred system of the Islamic Republic of Iran," said Rear Adm. Habibollah Sayyari, Iran's semi-official Mehr news agency reported. However, another semi-official Iranian news agency, ISNA, said the ships were on their way to Syria. CNN's Matt Smith and Shirzad Bozorgmehr contributed to this report