The BBC's Peter Morgan: The war is costing Bulgaria dear

Hundreds of riot police struggled to keep demonstrators opposing and supporting the measures apart as parliament debated the motion on Tuesday.

Bulgaria's parliament voted 154-83 to permit Nato flights along the country's western border with Yugoslavia after lawmakers argued the crisis in Kosovo must be settled quickly to prevent neighboring Macedonia from being destabilised by the tide of ethnic Albanian refugees.

Opposition has been vocal

About 10,000 people gathered to support the government in its pro-Nato stand, while around 2,000 demonstrated against it.

The vote was opposed by the Socialist Party of former communists and smaller leftist groups, who have organised a series of anti-Nato protests since allied bombings began 24 March.

Socialist leaders have accused the centre-right government of planning to push Bulgaria indirectly into what they call an illegal war.

Opposition to Nato action has been more vocal in Bulgaria since an American missile strayed off target and blew the roof off a house on the outskirts of Sofia last week.

The Bulgarian capital is just 50km (30 miles) from the border with Serbia.

Conflict hits trade

There has been concern in Bulgaria about the affect of the conflict on the country's economy.

More than half of Bulgaria's export trade used to cross into western Europe through Serbia. That trade route is now closed.

The destruction of bridges, blocking the Danube, has also hit exports.

Bulgaria's government estimates the conflict is costing the country's economy £10m a week.

BBC correspondent Peter Morgan said the country's already fragile economy was being stretched even further.