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Nato is taking its air offensive in Yugoslavia into a second week after rejecting an "unacceptable" ceasefire proposal from President Slobodan Milosevic.

With the humanitarian crisis deepening, UN Secretary-General Kofi Annan has spoken of his "profound outrage" at reports of ethnic cleansing in Kosovo by Serb forces.

Several countries have made pledges of aid to help the thousands of refugees who have fled Serbian attacks in Kosovo. A cargo plane carrying supplies is expected in Albania on Wednesday as part of the UK relief effort.

Rageh Omaar reports: "Round the clock bombardment"

European Union humanitarian affairs chief Emma Bonino is to travel to the region on Wednesday to assess the situation.

With widespread reports of Serb forces carrying out summary executions and setting fire to Albanian homes, plans to intensify the Nato operation are being considered.

However, poor weather in the region has again prevented RAF Harriers from carrying out their latest bombing mission against Serb targets.

Refugee children await their fate

For a second successive night a wave of GR-7 Harriers were force to abort an attack and return to their base in southern Italy as clouds hovered over their targets.

The RAF says all the planes returned safely, but they encountered some of the heaviest Serb anti-aircraft fire so far.

The Yugoslav news agency, Tanjug, said a series of explosions were heard southeast of the capital, Pristina and in the suburbs of Belgrade. It gave no details of damage.

There have been warnings from the Pentagon that after more than 1,000 cruise missile launches, stocks are "dwindling".

Offer falls short

Mr Milosevic made a conditional offer of a settlement over Kosovo through the Russian Prime Minister, Yevgeny Primakov.

He said he was ready to withdraw some forces from Kosovo if Nato halts air strikes on Yugoslavia.

But German Chancellor Gerhard Schröder told a news conference after meeting Mr Primakov in Bonn: "The proposals are no basis for a political settlement".

The United States said Mr Milosevic's pledges fell far short of what is needed to end Nato strikes.

Bill Clinton: We must remain determined with the will to see this through

President Clinton has for the first time said the slaughter of ethnic Albanians in Kosovo could undermine international support for Serb territorial claims to the province.

Urging allies to "remain steady and determined", he said: "If there was ever any doubt what is at stake in Kosovo, Mr Milosevic is certainly erasing it by his actions".

'Genocide' warnings

Jason Mills : "Refugees arriving at the Macedonian border have been sent back to Kosovo"

The diplomatic moves came as Nato said Serb ethnic cleansing had reached ''new heights'' and that it planned to intensify operations against Yugoslav forces.

Tens of thousands of refugees have poured out of Kosovo, leaving aid agencies struggling against the deepening crisis.

UN Secretary-General Kofi Annan has urged the world to help with the crisis asking Albania, Macedonia and Montenegro to keep their borders open.

"I appeal to all of Kosovo's neighbours to give shelter and comfort to the helpless civilians who have been driven from their homes," he said.

"Borders must be kept open, safety and protection must be given to those in need."

US State Department spokesman James Rubin warned there were indications that genocide was taking place.

Roads are reported to be clogged with fleeing civilians, many of whom have been forced from their homes at gunpoint.

In the last three days more than 80,000 refugees have reached Kukes on the Kosovo-Albanian border, recounting stories of Serb atrocities.

Executions

In Kosovo there are reports of summary executions, round-ups and massive expulsions.

Brian Hanrahan: "Outrage at refugee misery may harden Nato attitudes"

The UN refugee agency, UNHCR, say they fear ethnic cleansing could ultimately lead to a quarter of the population being driven out.

Nato is trying to confirm reports that Serbs are attacking refugees with artillery and tanks in the Pagarusa valley in central Kosovo.

Pec, a city of 100,000 residents in western Kosovo, is almost totally destroyed, says Nato spokesman Jamie Shea.