NATO gave the go-ahead Wednesday for 400 troops to deploy in Macedonia, the vanguard of a mission to disarm rebels.
But deploying a full 3,500-member NATO force depends on whether a cease-fire takes hold in the troubled Balkan nation.
The British servicemen and women from the 16 Air Assault Brigade will set out for Macedonia on Friday, most of them headquarters, communications and other support personnel, officials said.
The 19 NATO members approved the smaller force in an urgent meeting called despite a Roman Catholic holiday.
The 400-member contingent represents an attempt to find middle ground - avoiding the risk of sending in the entire force while fighting persists and at the same time moving quickly to support the fragile peace deal signed Monday.
NATO says that until there is a durable cease-fire, it won't send all 3,500 troops, including Americans, into Macedonia - where they will be in what are now front-line areas, collecting weapons from ethnic Albanian rebels.
The North Atlantic Council, NATO's ruling body, plans to meet again at the end of this week or early next week to decide on the entire deployment of the mission, code-named Essential Harvest.
The troops can be sent "once the council is satisfied the conditions for the deployment as stated before are completely fulfilled," NATO spokesman Yves Brodeur said.
Fighting has broken out each night in parts of northern Macedonia since the peace deal's signing by political leaders.
The Macedonian Defense Ministry said Wednesday there was fighting overnight between the insurgents and government forces in the second-largest city, Tetovo, and in surrounding villages.
The rebels also attacked government forces in the Kumanovo area, north of Skopje, and the soldiers returned fire. There was no word on casualties.
Still, Brodeur said "it's very positive since the signature of the agreement. Lots of things have happened and we are encouraged by what has happened so far."
The Macedonian government on Wednesday approved the deployment of NATO troops.
President Boris Trajkovski also asked parliament to begin the process of amending the constitution to give the ethnic Albanian minority greater rights - a key part of the peace plan.
The rebels have agreed to turn in their weapons, another requirement NATO set for the deployment.
But the alliance is still trying to get the rebels and the government to agree on how many weapons will be destroyed.
The rebels said they would surrender around 2,000 weapons. But Marjan Djurovski, a Defense Ministry spokesman, said a "fair and moderate estimate" would be that the rebels have at least 8,000 weapons.
Trajkovski also issued a statement offering amnesty to rebels who voluntarily surrender and did not commit war crimes, the second major condition of the accord.
The amnesty and the constitutional reforms are important incentives for the rebels, who did not sign onto the peace deal.
They launched their insurgency in February saying they sought greater rights for ethnic Albanians, who make up about a third of Macedonia's 2 million people.
While NATO wants to ensure calm on the ground before it deploys in force, it also is wary of waiting too long and having the deal fall apart.
"Events are unfolding quickly as NATO prepares to fulfill its promise to assist the Macedonian people by collecting arms and ammunition from the ethnic Albanian rebels," said Maj. Gen. Gunnar Lange of Denmark, a senior NATO representative in the Macedonian capital, Skopje.
NATO officials insist that this is a very narrowly defined mission, lasting only 30 days, and will involve collecting weapons being turned in voluntarily.
"Our soldiers will not come here to enforce peace," said Lange.
Military officials say that if the cease-fire collapses, NATO forces will withdraw.
In Washington, State Department spokesman Philip Reeker said a few hundred Americans would take part in the larger contingent.
He said they will be mostly support units - communications and medical support, among them - and will be drawn largely from forces already in the area.
The complete deployment of troops from Britain, the Czech Republic, France, Germany, Greece, Hungary, Italy, the Netherlands, Norway, Spain, Turkey and the United States, would take about two weeks, though the first weapons collection could begin earlier.
The mission will be led by Brig. Barney White-Spunner, 44, commander of the 16 Air Assault Brigade. White-Spunner previously served with British forces in Bosnia.