Tony Blair, the British prime minister, and James Baker, the co-chair of the Iraq Study Group, a bipartisan US panel, had suggested talks with the two nations to curb the violence in Iraq.

The US has previously accused Iran and Syria of helping to fuel the violence. Both have denied the accusations.

Rice told reporters: "There is no lack of opportunity to talk to the Iranians. I think the question is: is there anything about Iranian behaviour that suggests that they are prepared to contribute to stability in Iraq? and I have to say that at this point, I don't see it."

The US broke ties with Iran after students stormed the US embassy in Tehran in 1979 and held 52 Americans hostage for 444 days.

Mahmoud Ahmadinejad, the Iranian president, said on Tuesday that he was ready to talk to the US if there was a change in attitude from Washington.

'Syria with extremists'

Rice was also critical of Syria, saying it was "causing problems of extraordinary proportions in Lebanon", had undermined Mahmoud Abbas, the Palestinian president, and had "insulted" US allies, Egypt and Saudi Arabia.

She said: "That is not a very good record on which to suggest that just going and talking to Syria is going to get a change in their behaviour.

"There is no indication Syria wishes to be a stabilising force."

The US recalled its ambassador to Syria last year after the assassination of Rafiq al-Hariri, the former Lebanese prime minister.

Rice said: "Right now, it [Syria] appears to have aligned itself with the forces of extremism.

"I will talk to anybody, anywhere, any time, under the right circumstances if I think we can make progress.

"But we have had, over the course of this administration, discussions with the Syrians, talks with the Syrians, envoys to the Syrians, and nothing has ever changed in their behaviour."

She said she had been doing some "deep thinking" about US policy in Iraq but did not see any easy solutions to the violence there.

She said: "I don't think that there are any magic bullets about Iraq. This is a complicated place.

"They are in a very difficult time. It will take some combination of Iraqi responsibility for their politics and also ... increased responsibility for their security as well as better help from the neighbours in supporting Iraq as it makes this very difficult transition."