US soldiers collect their bags before loading into vehicles as they prepare to hand over their base to Iraqi forces in Iraq's southern province of Basra June 22, 2011.[Photo/Agencies]

The White House on Tuesday said time was running short for Iraq to issue a request for US troops to stay in the country beyond the end of this year.

"We are waiting ... to see whether or not the Iraqi government makes a request of us. That has not happened. We are obviously now in July," White House spokesman Jay Carney told reporters.

He said US troops were on track to leave Iraq by December 31, in accordance with a bilateral security pact, unless the government asked soon for troops to stay.

Mike Mullen, chairman of the US Joint Chiefs of Staff, said in April that Iraqi had only weeks to make the request to avoid a "physics problem" of moving 47,000 troops and related equipment.

"There is only so much time here available for the Iraqi government to make such a request," Carney said on Tuesday.

"If they do we will consider it, otherwise we are keeping on schedule."