NATO soldiers streamed into Macedonia on Thursday as part of a mission to help end six months of ethnic hostilities, even though the rival sides still have not agreed on how many weapons the troops should collect.

The British Royal Engineers who arrived in the capital, Skopje, were part of an airlift of 3,500 troops taking part in Operation Essential Harvest. The new troops joined an advance force of about 400 soldiers that began arriving Friday.

The main NATO task is to collect weapons surrendered by the rebels.

"The sooner we get on with it the better," said Capt. Keith Beddoe, who arrived with 91 other Royal Engineers. The engineers unloaded their personal gear and stood to the side of the tarmac, intently watching the unusually hectic air traffic.

NATO's ruling council decided Wednesday to approve the full deployment, including several hundred Americans in a behind-the-scenes role, despite scattered cease-fire violations since Macedonia's political parties signed a peace accord Aug. 13. The ethnic Albanian rebels did not sign the agreement but have agreed separately with NATO to disarm.

In Washington, State Department spokesman Philip Reeker welcomed the NATO action and said the United States looks to the insurgents to cooperate with NATO and to fully comply with all their commitments, including to voluntarily disarm.

Macedonia now has a real opportunity to avoid "a catastrophic civil war," he said. "The leaders and people of Macedonia must now fulfill the promise of peace by rapid implementation of the framework agreement."

Still, problems surfaced even before the deployment began.

Sporadic shooting incidents marred a fragile cease-fire, including an attack late Wednesday on a police checkpoint in the village of Mlin in northern Macedonia. Police forces responded. There were no injuries.

The government claimed Wednesday that the rebels have 85,000 weapons, while the rebels have said they're willing to hand over 2,000. Military and diplomatic officials want a deal before the weekend -- providing they can apply enough pressure to persuade both sides to accept a figure.

The mission's top military commander, Maj. Gen. Gunnar Lange, declined to speculate on the dispute, arguing that the collection process was more important than the actual number of weapons handed in.

"The rebels can re-arm. They can start fighting again," Lange said. "It's a lot more important that the trust and confidence that comes with the political process ... give them no wish to re-arm and start fighting again."

Mission commanders could begin picking up weapons from the rebel commanders sometime next week, NATO Secretary-General Lord Robertson said. The full deployment is expected to take up to 10 days.

The NATO mission is part of a comprehensive peace plan meant to end six months of fighting between the rebels and government troops. The plan also grants the ethnic Albanian minority greater rights.

The rebels took up arms in February, saying they were fighting for greater rights for Macedonia's minority ethnic Albanians, who account for about a third of the country's population of 2 million. Although the rebels have said they are ready to give up their struggle, the government fears they will fight on for a state of their own.