(Adds details, quotes, paragraphs 4-5, 13-18) By Carol Giacomo, Diplomatic Correspondent WASHINGTON, March 29 (Reuters) - U.S. aircraft carriers in the Gulf are not intended to provoke confrontation with Iran and Washington is committed to robust diplomatic efforts which are showing success, a senior U.S. official said on Thursday. The United States sent two carriers to the Gulf but "they are not there to provoke any kind of conflict with Iran," Undersecretary of State Nicholas Burns told the Senate Foreign Relations Committee, amid heightened sensitivity in the oil markets to growing tensions with Tehran. "We're convinced diplomacy is the way to proceed. We are most definitely on a diplomatic track. We do not believe that conflict with Iran is inevitable. We need to be patient and persistent," Burns said. His reassuramces and the administration's general approach drew praise from senators, including Democrat Joseph Biden of Delaware, the panel's chairman, who expressed fear about a "regional tinderbox that could ignite with one wrong move." "We need cool heads to prevail. We need patient, hard-headed diplomacy," Biden said. The United Nations hit Iran at the weekend with a second set of sanctions over its nuclear program, which the U.S. and its allies say is aimed at producing weapons and Tehran insists will be used to generate electricity. Washington and London also accuse Iran of backing insurgents battling their forces in Iraq. On Thursday, Britain sought international help to isolate Iran in a standoff over the capture of 15 military personnel in the Gulf, an incident which has raised tensions even more. Iran responded by delaying the planned release of a woman captive, indicating no speedy end to the stalemate. Burns said the seized British sailors and Marines were "entirely innocent" and were operating "clearly inside Iraqi waters." He said the Gulf was "not an Iranian lake (but an) international waterway." "We will protect the right of companies and nations to use the Gulf for international commerce and for it to be a peaceful region, not a violent region," Burns said. The U.N. Security Council targeted the new sanctions at Iran's arms exports, state-owned bank and elite Revolutionary Guards and threatened further penalties in 60 days if Tehran does not halt uranium enrichment. Under questioning, Burns acknowledged Iran's heavy dependence on imported gasoline was a "point of leverage" for the United States as it continues to pressure Tehran to rein in its nuclear program. Iran imported 150,000 barrels of gasoline per day in 2005, when its total consumption was 400,000 bpd, making it the second biggest gasoline importer after the United States, according to the U.S. Energy Information Administration. But a European diplomat told Reuters there had been "no definitive discussions yet" among major powers about sanctioning gasoline, which would be complicated by the fact that much of Iran's supply comes from India. While asserting Iran is moving aggressively to expand its nuclear capability, Burns insisted there is time -- which he did not quantify -- for diplomacy to work. He said U.S. pressure on international banks, companies and governments to cut back business and lending with Iran was stirring debate in Iran and undermining support for President Mahmoud Ahmadinejad.
