Iran can only be persuaded to co-operate over its nuclear programme "by peaceful means", Foreign Secretary Jack Straw has said.
Mr Straw said the situation in Iran was unlike that in Iraq
He told BBC Radio 4's Today Programme "nobody is talking about invading Iran", adding that "Iran is not Iraq".
Iran has removed UN seals at a nuclear facility, adding to international fears that it is developing atomic weapons.
But Mr Straw said there was no "categorical evidence" that a military use for the technology was planned.
'Action not discussed'
However, it was his "suspicion" that this was the case.
President Bush has said that options are open regarding Iran.
The foreign secretary told Today he understood people's "anxiety", adding: "No American president ever rules out options and that's just the way they are."
IRAN'S NUCLEAR STANDOFF
Sept 2002: Work begins on Iran's first reactor at Bushehr
Dec 2002: Satellites reveal Arak and Natanz sites triggering IAEA inspections
Nov 2003: Iran suspends uranium enrichment and allows tougher inspections
June 2004: IAEA rebukes Iran for not fully co-operating
Nov 2004: Iran suspends enrichment under deal with EU
Aug 2005: Iran rejects EU plan and re-opens Isfahan plant
Jan 2006: Iran re-opens Natanz facility
But he added: "I have never had a single discussion with anyone in the American administration about possible action."
Mr Straw said: "The point about Iraq was that it had invaded two of its neighbours, it had launched missiles against five of its neighbours.
"It incontrovertibly had had chemical, biological and nuclear weapons programmes.
"Now in the case of Iran, although we have a real problem with Iran it has not invaded any of its neighbours, it has not launched missile attacks against any of its neighbours, and nor so far as the nuclear weapon programme is concerned, do we have categorical evidence that it is developing a nuclear weapon."
The foreign ministers of Britain, France and Germany decided on Thursday to call an emergency meeting of the International Atomic Energy Agency so that it could consider reporting Iran to the Security Council.
Iran's president, Mahmoud Ahmadinejad, has dismissed the threat, saying the research would go on despite the Western "fuss".
Tehran says it broke the United Nations seals on the Natanz nuclear research facility on Tuesday because it wants to produce electricity, not because it is pursuing nuclear weapons.
But President Mahmoud Ahmadinejad said Iran would not be intimidated by "all of the fuss created by the big powers".
In October, he called for Israel to be "wiped off the map".
But Iran's foreign ministry later said Tehran respected the UN charter and had never used or threatened to use force.
Former Conservative deputy leader Michael Ancram has called for Iran to be excluded from the football World Cup this summer.