By Nick Childs
BBC Pentagon correspondent, reporting from St Petersburg
US Defence Secretary Donald Rumsfeld has said the activities of Iraqi Shia leader Moqtada Sadr and his supporters are unlawful and harmful.
Rumsfeld in Russia: Differences persist between the two countries
Speaking on a visit to St Petersburg, Russia, he said it was up to local coalition commanders and the Iraqi government to deal with the situation.
His Russian counterpart, Sergei Ivanov, said there is now an increased need for an international conference on Iraq.
Mr Rumsfeld has been visibly cautious recently in his comments on Iraq.
Whatever his private views, in public he seems to be almost deliberately maintaining his distance.
That may be a reflection of the sensitivities involved.
Asked in St Petersburg about the situation in the city of Najaf, and particularly the truce and talks going on there, Mr Rumsfeld said the behaviour of the Shia leader Moqtada Sadr and his supporters has clearly been unlawful and harmful to peace and order in the community.
He said there are competent coalition military officials working with the Iraqi government.
They certainly understand that, as he put it, it is important they do not allow independent militias to kill innocent men, women and children in the country.
But, he said, how they do that at any particular moment is up to them.
Mr Rumsfeld was speaking at a joint news conference with his Russian counterpart, Sergei Ivanov, who said Russia supports a peaceful solution to events in Iraq.
He added that the need for an international conference on the country, a Russian idea, has only increased recently.
More broadly, both men said they hoped for increased security cooperation between the United States and Russia.
But there are clearly still points of friction.
Mr Ivanov again said that he was, as he put it, reserved and negative about the recent entry of the Baltic states into Nato.
He also spoke of apprehension and worries about US support for Georgia.
And although it is not clear if it has come up in the talks so far, the two sides clearly still have differences over Iran.