The Ministry of Defence is reported to be resisting pressure from the Pentagon to move some of its troops to Baghdad.

The Americans are said to want British forces to share peace-keeping duties in some of the most violent regions of Iraq.

The moves are the consequence of the imminent Spanish withdrawal from Najaf.

Sources have predicted that the US military will formally request that British forces undertake "hearts and minds" operations in Baghdad.

The Tories have written to Tony Blair demanding urgent clarification on the matter.

Up to 1,700 extra UK troops could be deployed.

Downing Street refused to rule out extra forces being sent to Iraq, but a spokeswoman for Tony Blair stressed no decision to send extra UK forces had been taken.

She confirmed that Britain had been involved in talks about the consequences of Spanish withdrawal with its coalition partners.

Asked if the possibility of British troops moving further north had been considered, she replied: "I'm sure that would be looked at if decisions were taken to send more troops."