The announcement followed a published report that Foreign Secretary Jack Straw (search) had proposed the deployment of 5,000 more British troops in Iraq.
"In the light of events in Iraq over past weeks, the defense secretary has asked for a review of the forces and resources required to support U.K. operations," the Defense Ministry said.
"If any decisions are taken to adjust force levels, ministers will inform Parliament in the normal manner as they have done throughout the operation."
The ministry said that no decision to change troop levels had been taken.
Britain has 11,000 troops in Iraq. Forty-nine British soldiers have died in the war, with 11 of them killed since May 1 when President Bush declared an end to major fighting.
Earlier Thursday, Prime Minister Tony Blair's office said that the government "will ensure that the British presence in Iraq has the resources it needs to do the job that it's there for."
The Daily Telegraph newspaper on Thursday reported seeing notes drawn up for a meeting between Straw and Blair in which the foreign secretary urged sending more British troops to Iraq to help improve security.
The paper quoted Straw's notes as warning that "lack of political progress in solving the linked problems of security, infrastructure and the political process are undermining the consent of the Iraqi people to the coalition presence and providing fertile ground for extremists and terrorists."
The Foreign Office said it never comments on leaked documents, but added that "obviously the foreign secretary discusses Iraq with the prime minister on a regular basis."
Blair's office also said it wouldn't comment on a leak. The prime minister planned to hold his monthly news conference later Thursday.