Close U.S. ally Israel was unimpressed by the report, and
Prime Minister Ehud Olmert called for the U.S.-backed campaign to curb Iran's nuclear ambitions to press ahead regardless.
"It is vital to pursue efforts to prevent Iran from developing a capability like this and we will continue doing so along with our friends the United States," he told reporters.
Israeli Defence Minister Ehud Barak told Army Radio that as far as Israel knew Iran had probably renewed its weapons programme since 2003.
In Berlin, a spokesman said Foreign Minister Frank-Walter Steinmeier would discuss the report later on Tuesday with U.S. Secretary of State Condoleezza Rice.
China said its stand on Iran remained the same -- to seek a solution through dialogue. A foreign ministry spokesman said he hoped Iran could fulfil its U.N. resolution obligations and cooperate with the International Atomic Energy Agency.
A European security source familiar with intelligence on Iran said the change of American stance was welcome, and would undermine the position of U.S. hawks.
"The American agencies have in essence come closer to the position of the European ones," the source said.
"I think a political process (in dealing with Tehran) is more of an option than what we've perhaps been seeing from the hawks in the United States, the positioning for a military attack on Iran and so on."
The official said there was "no definitive proof either way" as to whether Iran had halted a nuclear arms programme in 2003. "And ... we keep seeing (Iranian) procurement attempts in Europe ... to acquire proliferation-relevant material."
World powers met last Saturday in Paris to discuss a further round of sanctions against Iran over its refusal to halt uranium enrichment, a process that can produce fuel for power plants or, potentially, nuclear weapons.
Two U.N. sanctions resolutions have been passed so far against Iran, unanimously but after diplomatic wrangling among the five permanent U.N. Security Council members -- the United States, China, Russia, France and Britain -- plus Germany.
Russia has been wary of harsh sanctions, arguing there is no evidence that Iran has sought to develop nuclear arms. Iran's top nuclear negotiator was meeting Russian President Vladimir Putin in Moscow on Tuesday.
Tension has escalated in recent months as Washington has ratcheted up the rhetoric against Tehran.
In Vienna, The United Nations nuclear watchdog said the latest U.S. intelligence report on Iran's nuclear weapons programme backed up the findings of IAEA inspectors over the past few years.
