Three policemen have been killed and about 100 people abducted or held hostage in a sudden escalation of violence in Macedonia.

The interior minister, Ljube Boskovski, said that all captives were reported released by midday yesterday.

The three men died on Sunday near the village of Semsovo, six miles outside Tetovo. They were members of a special unit called "the lions".

Another two policemen were badly hurt when a special police patrol was ambushed by ethnic Albanian rebels near the village of Trebos, also in the Tetovo area, police said.

The abductions came in the wake of the deployment on Sunday of a strong police force to secure a large area near Tetovo where Macedonian officials say one or more mass graves are located. However, a total of only 12 Macedonians have been reported missing.

The force was deployed after police found two assault rifles and five handguns in a vehicle at a checkpoint near Tetovo. Seven ethnic Albanians were subsequently arrested.

Yesterday, special police using armoured personnel carriers moved large reinforcements into the Semsovo area, where they found the vehicle of policemen hurt or killed in Sunday's ambush. Nearby, they found a sandbag position with two rifles.

In a statement yesterday, a dissident ethnic Albanian group calling itself the Albanian National Army claimed responsibility for the killings, saying: "The Skopje government is restarting its terror and sees war as the only response to Albanian demands."

It added: "The arrest of the seven Albanians has led to the killing of three Slav [Macedonian] paramilitaries and the wounding of more of them. It all happened in clashes with our units under commander Shqiponja 5 [Eagle 5]."

It urged Albanian politicians to pull out of Macedonian institutions and instead maintain political contacts with international representatives.

The Nato secretary general, Lord Robertson, said he had spoken to the Macedonian president and the Nato commander in Macedonia , adding: "I believe the situation has stabilised after the period of high tensions during the night."

Macedonian officials had earlier said that about 40 people in all had been abducted in the area, and another 60 or so Macedonians taken hostage in their village of Semsovo.

A western diplomat, speaking anonymously, criticised as "disproportionately large" the police operation to secure the alleged burial sites near Tetovo, which are suspected of containing the bodies of Macedonians killed by rebels during fighting earlier this year.

"This is a unilateral and completely unnecessary provocation," the diplomat added.

Tetovo, in the north-west, has been at the centre of Macedonia's crisis since fighting broke out in February.

Ethnic Albanian rebels had said they were fighting for more rights, but disbanded in August under a peace plan.

A former rebel commander who did not wish to be named said that the disbanded guerrilla group, the National Liberation Army, was not involved in the hostage taking.

"This is an act of irresponsible people who want to destabilise the situation," he said.