Britain today sounded a new warning to Iran that it was taking a "grave risk" if it did not end its banned nuclear programme and show the world it was not seeking to acquire the bomb.
Foreign Office minister Alistair Burt urged Tehran to avoid "miscalculations" over its nuclear capability and demonstrate its programme was for purely civil purposes.
Giving evidence to a House of Lords select committee, he also expressed "great concern" over Iranian attempts to develop a long-range intercontinental ballistic missile.
He said they already had weapons which could hit British forces in Cyprus and Afghanistan and were now seeking to acquire a missile which could reach Europe.
Prime Minister David Cameron discussed the mounting international concern over Iran's nuclear intentions with Barack Obama during their talks yesterday at the White House.
Mr Burt echoed a warning by the US President following the meeting that the prospects for finding a diplomatic solution to the crisis were "shrinking".
"We know that mistakes are made when information is uncertain and miscalculations end up being made," he said.
"What we do know for absolute certain is that the Iranians are on a track that has alerted the international community to a situation of great danger.
"It is not just the United Kingdom that is making calculations - so are others.
"In order to prevent miscalculations being made, the time is right now for the Iranians to take the opportunity that it is being presented to be thoroughly open about its programme and to convince the world that it only has peaceful intentions for its nuclear activities.
"If it does not, it is taking a grave risk."
While Britain like the United States, was still advising Israel that military action to destroy Iranian nuclear facilities was not "appropriate", he said "no options are off the table" if the regime fails to allay international concerns.
Mr Burt also highlighted concerns over Iran's missile programme after Mr Cameron said last week that it appeared to be seeking an intercontinental ballistic missile capability.
Iran already had the largest ballistic missile force in the Middle East, he said, with 200 to 300 medium range missiles - including the Shabab 3 - which had been tested to a range of 2,000 km.
"To put this into perspective, Cyprus and UK troops in Afghanistan fall well within that range along with Israel, Turkey and Saudi Arabia," he said.
"Iran also has ambitions to extend the range of its missiles which could give it the capability to target a number of European countries.
"In part, we believe this is supported by Iran's continuing development of a satellite launch programme.
"The fact that Iran continues to engage in this activity in defiance of UN Security Council resolutions - and particularly given unresolved concerns over the military dimension of its nuclear programme - is a cause of great concern."
He said the UK authorities were on the alert for "illegal and aggressive activity" by Iranian agents following the plot to assassinate the Saudi ambassador in Washington and their suspected involvement in attacks in Thailand, India and Georgia.
"We will remain vigilant to such activity by Iran and others and we have contingency plans for dealing with Iranian threats to UK interests," he said.