British soldiers are waiting today to learn if they will be ordered to relieve US troops in Iraq.
US military commanders have asked their British allies for help outside their normal areas of operation.
The British chief of the defence staff, General Sir Michael Walker, is expected to make a final recommendation to his government within the next few days, following a reconnaissance in Iraq today.
The discussions come as British Prime Minister Tony Blair holds talks today with UN secretary general Kofi Annan. It is the first time they have met since Mr Annan's recent warning that the war in Iraq was illegal.
Anti-war Labour MPs have seized on the possible deployment, with some arguing it is designed to give President George Bush a pre-election boost. But the British government has insisted it is a military decision.
Defence Secretary Geoff Hoon has refused to name the British units that could be involved, or the area they could be sent to, but has told MPs they would not be going to rebel strongholds in Baghdad or Fallujah.
PA