US President Bill Clinton said Nato would continue the campaign until its objectives had been achieved.

But in London, there have been calls for a diplomatic solution to the crisis while in Moscow the Russian parliament has backed Yugoslavia joining a Russia-Belarus Union.

Continuing confusion

Meanwhile there remains uncertainty over the exact circumstances surrounding the Nato strike on the convoy of Kosovo Albanian refugees.

The alliance has said one of its planes bombed one vehicle in a convoy. The Serbs said on Wednesday that more than 60 refugees had been killed in at least two attacks.

Nato cast doubt on whether footage broadcast by Serb TV showed their attack or another incident, or incidents, elsewhere.

The alliance said its aircraft had later attacked a second convoy, but had hit only military targets.

Some refugees in a third convoy reported that Serb aircraft had attacked them.

Jon Leyne reports: "Nato bombs spoke louder than words"

But Nato spokesman Jamie Shea said on Friday there was no new information. A video of the attack on the refugee convoy would not be made public until Nato had finished its investigation, he added.

Refugee expulsions stepped up

The UN refugee agency has said there is a danger of the entire Albanian population of Kosovo being driven out if expulsions by Serb forces continue at their present rate.

Nicholas Witchell reports on the questions which still remain unanswered

A spokesman for the UNHCR, Kris Janowski, said less than a quarter of the province's Albanians remain there.

He added that expulsions - which had slowed in the past two weeks - had now resumed with "full force".

John Simpson in Belgrade: The bombing is increasing President Milosevic's support

He said whole towns were being emptied by Serb forces. Over the past 24 hours, more than 12,000 people had crossed out of Kosovo into Albania and Macedonia.

Meanwhile, the BBC is launching Radio Link - a service aimed at reuniting Kosovan refugees separated from their families during the Balkan conflict.

Overnight strikes

On Thursday night, the town of Subotica, close to the Hungarian border, was bombed for the first time. Yugoslav media said Nato planes attacked two army barracks and damaged nearby houses.

Jacky Rowland reports: "People are trying to carry on with normal activities"

Other reported targets included oil refineries at Novi Sad and Pancevo on the outskirts of Belgrade and the capital's main airport.

In addition, Serb media said another bridge across the Danube - the fifth so far - had been struck.

But a Nato official denied Yugoslav news reports that missiles had struck a refugee centre in the Serbian town of Paracin. The official said aircraft had hit an ammunition dump in the vicinity.

(Click here for a map showing recent Nato strikes)

Montenegro under fire

In Montenegro, Nato warplanes bombed the capital, Podgorica, in their first daylight raid on the city - Nato had earlier said it would avoid hitting targets in Montenegro if at all possible

Montenegrin media reported missile strikes on an airfield outside Podgorica and a subterranean military base.

The Montenegrin Deputy Prime Minister, Dragisa Burzan, accused the Yugoslav army of provoking the Nato bombardment.

Calls for diplomacy

Kosovo ethnic Albanian leader Ibrahim Rugova has met Serbian President Milan Milutinovic and Yugoslav Deputy Prime Minister Nikola Sainovic in the Serbian Presidency building in Belgrade.

A correspondent for Sky News television who was present said Mr Rugova appeared "exhausted but well".

Nato has cast doubt on two previous reported meetings between Mr Rugova and the Yugoslav leadership, both earlier this month.

Paul Royall reports: "These strikes came from a publicly unwavering alliance"

Former UK Foreign Secretary Sir Malcolm Rifkind has called for a diplomatic solution to the Kosovo crisis, saying bombing alone is unlikely to succeed.

He said the diplomatic initiative had to be backed by the threat and use of ground forces and must include Russia.

Long campaign

Washington has reaffirmed its intention to continue the campaign until its objectives had been achieved.

President Bill Clinton said Nato would intensify its attacks on Yugoslavia.

And the White House indicated the bombing campaign could continue for months, possibly into the middle of the summer.

US Defence Secretary William Cohen said: "This is not going to be quick or easy or neat."

• Keep ground options open: Robertson
• Confusion continues over refugee bombing
• BBC launches refugee radio link
• Kosovo: The view from the US
• The Nato pilot's story