The United States, Britain and France turned up the pressure on Tehran on Thursday ahead of next week's release of a keenly awaited U.N. report that may offer new details about the military side of Iran's nuclear program.
Washington and its European allies suspect that Iran is developing the capability to produce atomic weapons under cover of a civilian nuclear energy program. Iran denies wanting atom bombs and insists its program is for generating electricity.
The report by the U.N. International Atomic Energy Agency (IAEA) is expected to unveil detailed intelligence pointing to military dimensions of Iran's nuclear program, while stopping short of saying explicitly that Tehran is trying to build such weapons.
"One (issue) in particular that I want to mention is the continuing threat posed by Iran's nuclear program," U.S. President Barack Obama told reporters ahead of a G20 heads of state summit in the French resort of Cannes.
"The IAEA is scheduled to release a report on Iran's nuclear program next week and (French) President (Nicolas) Sarkozy and I agree on the need to maintain the unprecedented pressure on Iran to meet its obligations," Obama said.
The United States, European Union and their allies around the world have imposed economic sanctions on Tehran for refusing to halt its uranium enrichment program, which Western powers believe is at the heart of an Iran atom bomb program.
The United States and Israel have repeatedly hinted at the possible use of force against Iranian nuclear sites, eliciting threats of fierce retaliation from the Islamic Republic.
The U.N. Security Council, with the backing of Iran's traditional sympathizers Russia and China, has imposed four rounds of increasingly tough sanctions on Tehran since 2006.
Responding to a newspaper report that Britain was stepping up military contingency plans amid mounting concerns about Iran, a spokesman for the British Foreign Office said on Wednesday that London was keeping all options open -- including the possibility of military action.
"We want a negotiated solution, but all options should be kept on the table," a Foreign Office spokesperson said.
U.S. WILLING TO USE "EVERY MEANS"
The report in the Guardian, without citing a source, said Britain's Defense Ministry believed the United States may accelerate plans for missile strikes at some key Iranian facilities and cited British officials as saying it would seek and receive military help from Britain for any mission.
U.N. diplomats in New York and government officials elsewhere called the Guardian report exaggerated. They said Israel would be more likely to use military force against Iranian nuclear facilities than the United States, which is bogged down in conflicts in Iraq and Afghanistan.
The pressure on Iran comes weeks after the United States accused Iran of plotting to assassinate the Saudi ambassador to Washington, an allegation Tehran denied.
U.S. State Department spokeswoman Victoria Nuland reiterated that the Obama administration was not closing the door on any options in dealing with Tehran's nuclear program.
"We have said many times in the last weeks and months that we do not seek a military confrontation with Iran," she said.
"That said, we are going to use every means at our disposal to continue to try to increase the international pressure on Iran to meet its IAEA obligations and to come clean on its nuclear program," Nuland told reporters in Washington.
Iranian Foreign Minister Ali Akbar Salehi told reporters in the Libyan city of Benghazi that Washington should avoid taking drastic steps against Tehran.
"We hope that they think twice before they put themselves on a collision course with Iran," Salehi said.
Diplomats in New York reiterated the West's commitment to a two-track strategy of negotiations aimed at resolving Iran's nearly decade-long nuclear standoff with the West and the threat of further sanctions should it refuse to cooperate.
Years of fitful negotiations with Tehran have gone nowhere. Depending on what the new IAEA report on Iran reveals, Western diplomats say they might have no choice but to try to expand the U.N. sanctions regime against Tehran.
There has been a surge of speculation in Israeli media this week that Prime Minister Benjamin Netanyahu is working to secure cabinet consensus for an attack on Iranian nuclear installations.
Israel bombed Iraq's nuclear reactor in 1981 and launched a similar sortie against Syria in 2007, precedents lending weight to its veiled threats to take similar action on Iran if foreign pressure fails to curb its nuclear program.
But many independent analysts see such a mission as too much for Israel to take on alone against Iran.
One senior Western diplomat said that international sanctions combined with sabotage operations like the Stuxnet computer virus that temporarily hobbled Iran's enrichment program have slowed Tehran's nuclear progress, reducing the need for the use of military force any time soon.
"Our policy of slowing things down has been successful, but it hasn't stopped it in its tracks," the diplomat said on condition of anonymity.
Analysts say a raid on Iran's nuclear facilities would wreak such damage on global prosperity and security that other means -- a mix of sanctions and sabotage -- must remain the levers of pressure on Tehran.
There are fears Iran could retaliate to an attack by temporarily severing the marine and pipeline arteries supplying a large part of global oil and gas demand.
Malcolm Chalmers, research director at Britain's Royal United Services Institute, described the impact of attacking Iran in stark terms: "You are talking about creating a wounded bear with very unpredictable consequences."
(Writing by Louis Charbonneau; reporting by Reuters bureaux worldwide; Editing by Vicki Allen)