Top foreign policy aides to US President Barack Obama played down the lack of concrete new steps in a joint statement by leaders of the world's major industrialized nations and hailed what they described as a united front.

"The discussion reflected, I'd say, a collective impatience with Iran and a desire to see real response going forward," US Deputy National Security Adviser Mark Froman told reporters on a conference call.

Another deputy national security adviser, Denis McDonough, highlighted the statement's warning that the next G8 meeting, in September, would be "an occasion to take stock" of progress towards freezing Tehran's atomic drive.

"I think it's a strong statement and it reflects a real sense of urgency on the part of all of us," US Undersecretary of State for Political Affairs William Burns said on the same conference call.

The joint statement says the leaders are "seriously concerned" about recent events in Iran, "deplore" the post-election violence there, warn that media restrictions and the detention of foreign nationals is "unacceptable," and warn against interference with embassies in the Islamic republic.

On the nuclear front, the leaders again endorsed the diplomatic track, while warning Tehran to comply with UN resolutions calling for a freeze on its uranium enrichment activities "without further delay."

"We condemn the declarations of (Iranian) President (Mahmoud) Ahmadinejad denying the Holocaust," the statement says.

"It's reflective of impatience with Iran," said McDonough.

"The president (Obama) was struck by the unanimity around Iran," the official said.