The London talks by senior officials come amid mounting tension after Iran sent its first rocket into space Sunday and hardline President Mahmoud Ahmadinejad said that the nuclear program had no "reverse gear."

The comment drew a simple retort from US Secretary of State, Condoleeza Rice, who said: "They don't need a reverse gear. They need a stop button."

A low-key meeting

On the eve of the talks, the United States reaffirmed its offer of direct talks with Tehran -- but a report claimed Washington is

stepping up covert operations in Iran in a new strategy that could spark an "open confrontation."

US Under Secretary for Political Affairs Nicholas Burns was to hold talks in London with counterparts numbers from Britain, China, France, Germany and Russia, to hammer out how best to persuade Tehran to comply with United Nations demands.

The UN imposed a first round of limited economic sanctions against Iran in December after it refused to comply with an earlier demand to suspend enrichment activities.

Now the six countries -- the five permanent members of the UN Security Council plus Germany -- must decide on how to respond to the lapsing of a 60-day deadline.

The US, France and Britain want the Security Council to impose fresh sanctions but Russia and China, which hold veto rights and have economic, energy and strategic interests in Iran, are reluctant to pile on the pressure.

The London talks are expected to lay the groundwork for a Security Council meeting which could take place within the next

week.

The Foreign Office said the meeting would be low-key, with no decisions on action in relation to Iran expected to be announced.

"This is very much an initial discreet discussion at senior official level to discuss further measures on Iran," a spokesman said. "Officials will want to discuss any conclusions that arise out of the meeting with ministers in their capitals."

The International Atomic Energy Agency, the UN's nuclear watchdog, confirmed Thursday that Iran had ignored the Security Council's demand to stop enriching uranium -- a possible route to developing nuclear weapons -- and had expanded its nuclear program.

Russia worried about military strikes against Iran

Condoleezza Rice said Sunday that she was confident the six nations could find common ground and again offered to hold negotiations with Iran if it suspends enrichment.

"We're leaving open the track of negotiations, because the best way to resolve this would be to have Iran come to the table," she added.

Her remarks came after US Vice-President Dick Cheney fuelled fears that the Bush administration could use military strikes

against Iran.

"All options are still on the table," he said, during a visit to Australia Saturday, while stressing that the US favored a diplomatic solution to the problem.

On Monday, Russia's Foreign Minister Sergei Lavrov said on Monday he was worried by talk of possible military strikes against Iran, Interfax news agency reported.

"Forecasts and suggestions about a military strike on Iran have become more frequent and this is worrying," Lavrov was quoted as saying during a meeting with President Vladimir Putin.

The United States, while insisting it has no military plans against Iran, is beefing up its naval firepower in the Gulf: two US aircraft carrier groups are now there -- the highest concentration since the 2003 invasion of Iraq.

And The New Yorker magazine reported Sunday that the United States is stepping up covert operations in Iran in a new strategy that risks sparking an "open confrontation" and benefits Sunni radicals.

The weekly's Seymour Hersh reported that the US Defense Department has formed a special planning group to draw up possible attacks on Iran "that can be implemented, upon orders from the president, within 24 hours."

"Height of the Cold War"

Tehran insists that its uranium enrichment program is designed to fuel power stations for civilians.

Deputy Foreign Minister Manouchehr Mohammadi said Sunday that Iran was "ready for negotiations without preconditions with the United States, but the Americans have not accepted it yet."

He added that, even if the Security Council adopted a second resolution, Tehran would press on with its nuclear program.

The West's stand-off with Iran is like "the height of the Cold War," Britain's most senior naval officer said in an interview with The Daily Telegraph newspaper published on Monday.

"There are extra challenges facing us," Commodore Keith Winstanley said. "There have been a series of Iranian exercises in the northern Gulf to the point that it's a bit like with the Russians at the height of the Cold War," he said.

"We just have to hope that's not a recipe for miscalculation."