Two rockets were fired at a military base housing US troops near Baghdad airport, in the 10th such attack since October, the Iraqi army announced Thursday (December 12th).

There were no casualties in the overnight attack, which follows one on the same base on Monday which wounded six members of Iraq's elite counter-terrorism force, two of them critically, the army said.

The US has expressed mounting concern about the number of attacks on US bases and diplomatic missions, several of which it has blamed on militia groups trained by Iran.

Security sources linked at least one attack last week to Kataib Hizbullah, a powerful Iraqi militia close to Tehran and blacklisted by Washington.

Iran holds vast sway in Iraq, especially among the Popular Mobilisation Forces (PMF), which it has largely organised and trained.

A US defence official told AFP the rocket attacks made the PMF a bigger security threat to American troops in Iraq than the "Islamic State of Iraq and Syria" (ISIS), which the US has vowed to help Baghdad wipe out.

On Friday, the US imposed sanctions on three senior PMF figures.