Washington warned Thursday that it would not tolerate attacks on US interests in Iraq by Iran-backed militias, as Baghdad worries about a possible US withdrawal.

"We can't tolerate the threats to our people, our men and women serving abroad," said David Schenker, assistant secretary of state for near Eastern affairs.

Schenker did not officially confirm a reported US threat to withdraw its troop and close its embassy in Baghdad unless the attacks against them stop.