The Blair government has said it will send up to 12,000 more troops to strengthen NATO ground forces in Macedonia. The announcement followed NATO's decision on Tuesday to expand the size of the forces preparing to enter Kosovo from 28,000 to 60,000.

Britain was the first country to specify how many additional troops it will send, despite NATO's military commanders remaining undecided about the exact number of extra troops needed. The UK already has 5,400 troops deployed in Macedonia and a further 1,600 committed to Kosovo operations. Some 700 Scots commandos have been put on 72-hour notice to go to Kosovo. Together with the Royal Gurkha Rifles, paratroopers from the 1st Battalion, and several other divisions, this will bring Britain's military forces in the area up to 18,000.

The UK will probably be the largest single contributor to “Operation Joint Guardian”, which is under the command of the British General Sir Michael Jackson. The Defence Ministry said there was no intention at this stage to call up Territorial Army (volunteer) units, although individual TA members could be asked to go.

Announcing the additional forces, Defence Minister George Robertson said it was a momentous undertaking “which in the coming months and years will require a major investment of diplomatic, financial, humanitarian and military effort." Nonetheless, Britain's contribution “is consistent with the role we have taken so far in the campaign", he said.

In the last weeks, Prime Minister Tony Blair has been advancing increasingly bellicose demands for NATO and the US to launch a ground war against Serbia. His calls reportedly led to clashes with US President Bill Clinton and provoked outspoken criticism from other European countries, which are more concerned at the potential backlash from the public. Although Blair denied a rift, saying that ground troops should only be used in a “permissive environment”, significant sections of the military elite, such as retired US General Colin Powell, insisted that NATO must “go all-out” to win.

Defence Minister Robertson was at pains to deny that the expansion was intended to prepare the way for NATO to fight its way into Kosovo, claiming that the additional troops were necessary to help returning refugees, clear land mines and distribute aid. “This is not an invasion force. It is a peace implementation force," he said.

Whilst even the increased numbers would not provide sufficient strength for NATO to fight its way into the province against significant armed opposition, military sources have indicated that they could provide the core of an invasion force, should such a decision be taken. Robertson acknowledged that the troops will enter "what may well be a tense and hostile environment inside Kosovo."