We want to prevent what can be limited, localised skirmishes becoming bigger or spilling over into the wider region

Nato chief Lord Robertson

In continued violence in the region, a Macedonian policeman has been killed in an attack on a police convoy near the border with Kosovo.

And in Brussels, Nato gave the green light for Yugoslav forces to enter part of the demilitarised zone between Kosovo and southern Serbia in the area where it joins the border with Macedonia - a move also aimed at stemming the rebels' activities.

The developments follow days of growing tension in the region.

Reports say that several hours of fighting preceded the US entry into Tanusevci.

US troops moved in to Tanusevci and found it deserted

"We have just concluded a successful operation by eliminating a safe haven for armed groups here in Kosovo," the commander of US peacekeepers in the province, Brigadier General Kenneth Quinlan, told reporters.

The BBC's Nick Wood in Tanusevci reported that the US troops crossed the border into Macedonia during the operation, but US officers said they had occupied only parts of the village on the Kosovo side of the frontier.

"Not a single US K-For soldier entered Macedonia," a Nato official in Brussels said.

Macedonian Prime Minister Ljubco Georgievski had earlier invited K-For into the Macedonian parts of the village.

This is maybe one more proof of how inefficient... K-For has been

Yugoslav President Vojislav Kostunica

In the other major break with existing Nato policy, military planners in Brussels decided to allow Yugoslav troops back into part of the buffer zone, dividing Kosovo from the rest of Serbia, in another bid to control rebel activity.

"At the moment these skirmishes are of concern," said Nato Secretary-General Lord Robertson. "We want to prevent what can be limited, localised skirmishes becoming bigger or spilling over into the wider region."

BBC Defence Correspondent Jonathan Marcus says it is a significant step for Nato. Officials believe it is needed to combat the rebel threat.

Yugoslavia says it will move into the "dangerous" border zone

Yugoslav President Vojislav Kostunica accepted the offer to move in to what he called a "very dangerous" area, but said it highlighted the failure of Nato to secure the zone.

"This is maybe one more proof of how inefficient in all these years... K-For has been," he said.

The rebels have warned that opening the zone to Yugoslav forces will lead to a worsening of the violence.

Weapons

K-For commanders will decide how much freedom of movement the Yugoslav forces will have inside the 5km-wide (three mile) zone, and what kind of weapons they will be able to use.

Macedonia has asked for a similar buffer zone to be created along its own border with Kosovo, but the UN Security Council rejected the idea on Wednesday.

The rebels, who want to unite parts of Serbia and Macedonia where ethnic Albanians live, have attracted strong international condemnation.

The Albanian president has described their activities as "totally unacceptable", and Macedonia - where ethnic Albanians make up nearly a third of the population - fears a major new conflict.

Correspondents say some of the rebels are veterans of the Kosovo Liberation Army (KLA), which fought against Yugoslav forces, and are disappointed not to have won Nato's support for their insurgency.

The main guerrilla grouping is known as the National Liberation Army, which has the same initials in Albanian as the KLA.