US combat troops may stay in northern Iraq after a deadline for them to pull back by the end of June has passed, the top US commander in the area has said.

Col Gary Volesky said his soldiers would stay in Mosul and other nearby cities where al-Qaeda remained a threat if the Iraqi government asked them to.

US and Iraqi officials describe Mosul as al-Qaeda in Iraq's last major urban stronghold in the country.

Barack Obama has said he wants all US troops out of Iraq by the end of 2011.

"If the Iraqi government wants us to stay we will stay," said Col Volesky in a teleconference with journalists.

He said the US military was conducting an assessment of the situation in Mosul after five US soldiers were killed in a suicide lorry bombing there on Friday.

In January, Ryan Crocker, the outgoing US ambassador to Iraq, warned that a hasty withdrawal of US troops from the country would create "severe risks".

He said al-Qaeda remained a threat and that an overly rapid departure would have a "chilling effect" on Iraqis.

The US currently has more than 140,000 troops in Iraq, and combat troops are due to pull out of Iraq's cities by the end of June.

Under a recent agreement, they are expected to remain elsewhere in the country until the end of August 2010.