The US military commander in Iraq has accused Iran of inciting violence there and said Tehran's ambassador to Baghdad was a member of the Revolutionary Guards Qods force.
Gen David Petraeus, speaking at a US military base near the Iranian border on Saturday, said Iran was giving militia groups advanced weaponry and guidance.
"They are responsible for providing the weapons, the training, the funding and in some cases the direction for operations that have indeed killed US soldiers," Gen Petraeus said when asked if the Iranian government was responsible for killing US troops.
Washington accuses Iran's Revolutionary Guards' elite Qods force of supporting militias who have attacked US troops.
Iran dismissed Gen Petraeus's comments as "baseless".
The US military also said it had caught three Iranian- backed "special groups militia" believed to be behind the kidnapping of five Britons in a May raid blamed on Shia militiamen loyal to anti-American cleric Moqtada al-Sadr.
There is no word on the Britons' fate.