Contingency planning for sending more British troops to Iraq is at an advanced stage, the BBC has learned.
More British troops may be deployed in the next month or two
Around 800 extra soldiers could be deployed in June or July, say defence sources.
Top brass from the UK military were in Iraq last week and it is understood they were examining Britain's options.
These could include expanding the UK presence in the Iraqi provinces of Najaf and Qadifiyah. But no final decisions have been taken.
Royal Marines from 40 Commando were already due to go to Iraq in July as part of the regular rotation of British troops in the south of the country.
But their role is now expected to change, with them being sent instead to Najaf. That would mean other troops would need to be found for the regular rotation.
There are currently around 7,900 troops in Iraq. Defence sources say any further deployment will not be "rushed" and are warning that no announcement is imminent.
The move follows the decision of Spain, Honduras and the Dominican Republic to withdraw troops from Iraq.
Conservative shadow defence secretary Nicholas Soames on Thursday protested that newspapers had already been told before Parliament about the extra troop deployments.
Commons Speaker Michael Martin told MPs the House of Commons should be told about any "significant increase" in the number of troops being sent to "areas of danger".
Liberal Democrat foreign affairs spokesman Sir Menzies Campbell said the extra troops might find themselves serving alongside US forces whom he said had a "different culture" to their British counterparts.
"My anxiety would be that if British forces were sent to Baghdad and were under the direct operational command of an American commander, then they might find themselves in the position of having to decide whether or not to accept an order or whether to rely on their own instincts and training," he said.
Sir Jeremy Greenstock, Britain's former special representative in Iraq, told BBC Radio 4's World At One the alleged abuses of Iraqi prisoners by coalition forces had made it likely the coalition would have to stay longer in the country.
At a news conference with Polish President Aleksander Kwasniewski, Tony Blair condemned alleged abuses in his strongest language so far.
of prisoners, the torture of prisoners, degrading treatment of people in the
custody of coalition forces, these things are completely and totally
unacceptable," he said.
"They are inexcusable, and there can be no possible justification
Everything possible had to be done to root out such practices, said Mr Blair, who also paid tribute to the thousands of coalition troops who were risking their lives to help the people of Iraq.
Mr Kwasniewski said that the 2,500 Polish troops working in Iraq would not be withdrawn
until some degree of order had been restored.
"We need to fulfil our mission ... We will do nothing that can possibly
increase the chaos in Iraq," he said.