The U.S. on Tuesday joined other major world powers in urging Iran to curb its nuclear program, in a statement notable for its moderate language and for its commitment to diplomacy to defuse the atomic standoff.

Diplomats at the International Atomic Energy Agency's 35-nation board meeting said they could not remember such a joint statement from Washington, Moscow, Beijing and the three big European powers in Vienna. The statement urged Tehran to heed U.N. Security Council demands to limit its nuclear activities and thereby reduce fears it was trying to make atomic arms.

Under the previous U.S. administration, Washington's push for harsh language condemning Iran for refusing to freeze its uranium enrichment program — and its implicit threat of force if negotiations failed — was opposed by Russia and China. That doomed attempts to forge a common stance at board meetings focusing on Iran.

Tuesday's statement appeared to reflect President Barack Obama's commitment to turn from cold-shouldering Tehran on nuclear issues and trying to reach common ground in direct talks.

While the language was softer than Washington favored in the past, it was more direct than what China had been previously willing to endorse.

That appeared to reflect an apparent readiness by Beijing to shift its stance in response to America's newfound willingness to embrace moderation in dealing with Tehran.

The six-paragraph statement urged Iran "to implement the resolutions of the U.N. Security Council" — without threatening further sanctions if it does not, as the U.S. had done at past board meetings.

The statement echoed IAEA concerns about Iran's stonewalling of agency efforts to probe allegations that it at least had drafted plans for nuclear weapons in the past. The statement urged Iran to cooperate in the investigation and came down squarely on the side of negotiations to solve the impasse.

"We remain firmly committed to a comprehensive diplomatic solution, including through direct dialogue," said the statement, also signed by Germany, Britain and France, and read by French representative Olivier Caron. He urged Tehran "to take this opportunity for engagement with us and thereby maximize opportunities for a negotiated way forward.

Harsher language was left to the European Union which expressed "grave concern" at Iran's defiance of the Security Council.

"We deeply regret the continued lack of cooperation by Iran" with the IAEA probe of its past activities, said the EU statement.

It said the EU would continue to pursue an "active dual track policy;" shorthand for negotiations coupled with the threat of sanctions.

Iran, which has been under IAEA investigation since 2002, denies any interest in trying to make nuclear weapons, saying it wants to harness the atom only to generate energy.

It continues uranium enrichment, which can create both nuclear fuel and the fissile core of nuclear warheads, despite three sets of Security Council sanctions.