The White House ruled out an "arbitrary date" for troop withdrawals
Iraq and the US have called for an agreement on a "general time horizon" for the withdrawal of US troops from Iraq, the White House has announced.
The call comes after a video conference between President George W Bush and Iraqi Prime Minister Nouri Maliki.
The two governments are currently negotiating an agreement to allow US forces to remain in the country.
Any decision to remove troops would be based on "improving conditions", not an "arbitrary date", the White House said.
"Improving conditions should allow for the agreements now under negotiation to include a general time horizon for meeting aspirational goals - such as the resumption of Iraqi security control in their cities and provinces and the further reduction of US combat forces from Iraq," said White House spokeswoman Dana Perino in a statement.
Swipe at Obama?
The BBC's Adam Brookes in Washington says the announcement is designed to encourage the idea that US troops are coming home, without committing to any dates.
Our correspondent notes that the reference to an "arbitrary date" could well be a swipe at Democratic presidential hopeful Barack Obama's plan to withdraw combat troops from Iraq within 16 months of taking office.
The announcement comes after Mr Maliki raised the prospect of setting a timetable for the withdrawal of US troops as part of negotiations over the new security agreement with Washington.
The current mandate for America's military presence - based on a UN resolution - expires on 31 December 2008.