US: The US Vice-President, Mr Dick Cheney, has said Iran is at the top of the administration's list of world trouble spots.
He also expressed concern that Israel "might well decide to act first" to eliminate any nuclear threat from Tehran.
"You look around the world at potential trouble spots, Iran is right at the top of the list," Mr Cheney said in an interview aired on MSNBC.
Mr Cheney, one of the chief architects of the Iraq war, said the administration would continue to try to use diplomacy to address what he said were serious concerns about Iran's nuclear weapons programme and ties to terrorism.
The administration has also accused Iran of interfering in the affairs of neighbouring Iraq, where US forces have been bogged down in an insurgency since the 2003 invasion.
If Iran resisted demands to rein in its nuclear programme, Mr Cheney said the next step would be to take the matter to the UN Security Council and seek international sanctions "to force them to live up to the commitments and obligations".
Mr Cheney described Iran's nuclear programme as "fairly robust".
Iran denies its nuclear facilities are to be used to make weapons.
Mr Cheney, who was a leading advocate for the Iraq invasion,said one concern was that Israel might act against the Iranians "without being asked".
"If, in fact, the Israelis became convinced the Iranians had significant nuclear capability, given the fact that Iran has a stated policy that their objective is the destruction of Israel, the Israelis might well decide to act first, and let the rest of the world worry about cleaning up the diplomatic mess afterwards."
Israel set a precedent for such action in 1981 when it sent warplanes to destroy Iraq's French-built Osiraq reactor, seen as the key to Saddam's nuclear ambitions.
"We don't want a war in the Middle East if we can avoid it. And certainly in the case of the Iranian situation, I think everybody would be best suited by or best treated and dealt with if we could deal with it diplomatically," said Mr Cheney.
Like Mr Cheney, President Bush has stressed the importance of diplomacy in dealing with Iran, but said this week: "I will never take any option off the table."
The Bush administration imposed economic penalties this month against Chinese companies it accused of helping Tehran improve its longer-range ballistic missiles.
The New Yorker magazine reported this week that the US has been conducting secret reconnaissance missions inside Iran to help identify potential nuclear, chemical and missile targets. The White House and Pentagon have disputed the report.