The UK Defence Secretary Geoff Hoon says 850 British troops are to be sent to a US-controlled region of Iraq close to the capital.
The troops will fill in behind US marines when they carry out an anticipated strike on the rebellious city of Falluja.
Below are some reactions to the announcement.
Richard Boucher, US Department of State spokesman:
It just demonstrates, once again, the kind of role that Britain is prepared to play in a matter that affects their security and our security, the security of all of us, and that is stabilising Iraq and helping the people of Iraq take control of their destiny
and reconstruct their country.
Geraldine Smith MP, Labour (former supporter of war and one of more than 60 Labour MPs who called for a parliamentary vote on the deployment):
We're being told that this is an operational necessity, and if this is true it must imply that the Americans have insufficient of the right type of troops and equipment on the ground in Iraq. And we really need to know why this is so. After all, they are the world's superpower. It does beg the question is it because George Bush is not prepared to commit additional American forces before the presidential elections?
Dave Prentis, general secretary of UK's biggest union Unison:
[The defence secretary] should recognise the damage that could be done to the reputation of the
British army, and draw back from support for US military adventurism.
Nicholas Soames, shadow defence secretary:
We will support this deployment on the basis of its being a
necessary, operational military contribution to the coalition's efforts to bring peace and stability to Iraq ahead of the January elections...
This House [parliament] and the nation can be supremely confident that the Black Watch, the Royal Highland Regiment, who bear the distinction of Baghdad 1917 as one of their battle honours, will carry out their task with all the fortitude, discipline and courage we would expect from one of the finest regiments in the
British Army. To them and to all the supporting arms that go with them in the battle group we wish God speed.
Tommy Sheridan, Scottish Socialist Party national convenor:
Tony Blair is committing an unforgivable crime, sending brave young Scots to cover the back of George Bush as he attempts to look tough just in time for the US elections in two weeks' time.
Is this the blood price Tony Blair is willing to pay, young Scottish soldiers sacrificed in a disastrous war justified on deceit and lies?
I would appeal for the families of Black Watch soldiers to join with the campaign launched by Rose and Maxine Gentle [mother and sister of UK soldier killed in Iraq] to have all coalition troops withdrawn from Iraq by Christmas.
Bruce George MP (Labour), Defence Select Committee chairman:
The idea that the military makes decisions is a fantasy.
They can advise but ultimately it is a politician, the secretary of state, the prime minister, the Cabinet committee, who rejects or accepts the recommendation.
I think we should be honest and say it is a political military decision because the military cannot operate in a political vacuum.
Black Watch officer, Basra, Iraq:
We're up for it.
Dennis Skinner MP (Labour):
You don't have to be a lover of Saddam Hussein to be against this deployment and against the war.
We are mirroring the views of millions of people in Britain, that is valid reason enough.
Don't you think it is slightly ironic that the American president and his vice-president, who both refused to face the muck and bullets in Vietnam, are
now calling upon British forces to bail them out?
Alice Mahon MP (Labour):
It's mission creep. I was totally unconvinced by the arguments used by Geoff Hoon. I heard nothing that explained why this requires British and not American troops. This is a political decision.