In the single biggest massacre since NATO-led peacekeepers entered Kosovo six weeks ago, 14 Serbian farmers were killed last night near the town of Lipljan in central Kosovo, NATO officials said today.

The incident indicates that ethnic tensions persist in areas such as Lipljan, one of a dwindling number of mixed communities of Serbs and ethnic Albanians, and it may accelerate an already large exodus of Serbs from Kosovo.

According to NATO officials, around 9.30 p.m. last night, British troops heard gunshots near the village of Gracko about one mile south of Lipljan. Forty minutes later, British soldiers found the bodies of 13 Serbian farmers, all men.

All 13 had been shot near a combine harvester outside Gracko. About 150 yards away, a 14th man was found shot dead near a tractor, NATO officials said.

Tensions have been high in the Lipljan area for weeks. Serbs from outlying villages have settled there to find more security. Some ethnic Albanians have gained a reputation for militant opposition to their presence.

A few weeks ago, one ethnic Albanian was arrested for firing a shotgun into a Serbian house; Serbs responded by strewing hand grenades downtown on market day. They failed to detonate. A British officer there reported "a near riot" of the two groups before the attacks.

"Hard-line groups want to see the Serbs leave," he said. "There is also a mafiosi element at work," attempting to gain control of Serbian businesses in the town. This morning NATO troops had sealed off the area around the killing and moved the bodies to the morgue in Pristina.

In a statement, the international peacekeeping force said it condemns "this despicable act and calls upon leaders of all communities in Kosovo to do the same."