Unknown gunmen have launched a mortar attack on a US military airbase in northern Iraqi city of Kirkuk.
It was not immediately clear whether the attack caused any casualties or damage to the airbase north of the Iraqi capital, Baghdad.
Earlier in April, a US military base in Iraq's southern city of Nassiriya also came under a rocket attack.
There are currently about 50,000 US soldiers stationed in Iraq and are due to leave the country by the end of this year, in line with the 2008 US-Iraq Status of Forces Agreement (SOFA).
The US led the invasion of Iraq in 2003, under the pretext that its former dictator Saddam Hussein was in possession of weapons of mass destruction. Although no such weapons were ever found in the country, the massive US-led forces remained in the country for year, leaving behind a long trail of civilian casualties, displacements and major destruction.