Washington has welcomed a call from the United Nations nuclear watchdog that Iran should allow stricter inspections of its nuclear facilities.
ElBaradei: Iran should be transparent
The International Atomic Energy Agency - which monitors nuclear programmes around the world - urged Iran to be transparent about its nuclear objectives, in order to reassure the world it was not developing nuclear weapons.
It came a day after US President George W Bush urged the world to warn Tehran against developing such weapons.
The report fell short of US demands that the agency condemn Iran - but Washington quickly gave its backing.
The director general of the IAEA, Mohammed ElBaradei, said Iran should sign an additional protocol to the Nuclear Non-Proliferation Treaty (NPT) as soon as possible and without conditions.
Allows for inspections at short notice
IAEA can take environmental samples at any location
The protocol would allow for more intensive and short-term inspections of Iranian nuclear facilities, and Mr ElBaradei urged more co-operation for inspections teams, who are due to return to Iran shortly.
"Iran should continue to be fully transparent," he said.
White House spokesman Ari Fleischer told reporters: "Iran needs to comply.
"Otherwise the world will conclude that Iran may be producing nuclear weapons."
A top Iranian official said the report showed that Iran's nuclear programme was peaceful.
"The policy of the Islamic republic is not to produce nuclear arms," said Gholam Reza Aghazadeh, the head of Iran's Atomic Energy Agency.
"The United States wanted to obtain a resolution condemning Iran, but the efforts of our friends, our arguments and the discussions that we conducted, resulted in a failure for the United States."
Observers said the statement by the IAEA board of governors, which followed a meeting in the Austrian capital Vienna, was a compromise designed to placate both sides.
Iran's representative at the IAEA, Ali Salehi, said Iran would not accept further inspections of sites and had "dissociated" itself from that part of the statement.
He also said there was no consensus within the board on whether Iran should unconditionally accept tougher inspections.
However, Mr Salehi added that although his country was still considering whether to sign the protocol he would continue to co-operate with the agency.
Russian Deputy Foreign Minister Yury Fedotov said the IAEA board had adopted a "balanced declaration".
"[The board] on the one hand noted that Iran did not reveal all its nuclear material and programmes, but on the other hand noted that Iran was taking steps to redress the situation," he said.
Russia is helping Iran to build an $800m nuclear reactor in the south-western Iranian port of Bushehr.