Fifteen people died after the daylight Nato strike, which hit a hospital and market place.

"This morning [Friday] Nato aircraft carried out an attack against Nis airfield using combined effects munitions [cluster bombs]. Unfortunately, it is highly probable that a weapon went astray and hit civilian buildings," a Nato military statement said.

Serb media and witnesses described the attacks on Nis - Yugoslavia's third city - as the heaviest of the campaign.

On Friday night, air raid sirens sounded again in Belgrade, and a BBC correspondent in the city confirmed that an attack was taking place - the first on the capital for several days.

The Western alliance has been pressing ahead with its bombing campaign, as negotiations with Russia for a Kosovo settlement continue.

John Simpson: "The streets were full of shoppers when a bomb hit the market-place"

BBC Correspondent Mike Williams, who visited Nis, says 15 people were killed after bombs hit two areas of the city about 11am. on Friday.

Local officials say 60 have been injured.

Our correspondent says he saw bodies lying in the market place and in a residential street near a hospital, with unexploded cluster bombs lying in the gardens of people's homes.

The daylight attack hit crowded streets, as people were no longer in the bomb shelters where they had spent the night.

Hospital hit

The BBC's Mike Williams witnesses the carnage in Nis

Our correspondent confirmed a bomb had hit the hospital, apparently injuring five people, but there are no reports of deaths in the hospital.

John Simpson: "The streets were full of shoppers when a bomb hit the market-place"

Nato says it had not targeted a civilian hospital, but is investigating the incident.

The airport outside Nis was hit during Thursday night's bombing.

Other targets on the 44th night of Nato's air offensive included a bridge on the main railway line from Belgrade to Bucharest, and targets in the second city, Novi Sad.

(Click here to see a map of last night's Nato strikes)

New planes

The strikes came as the United States announced it was sending a new wave of aircraft to join the campaign against Yugoslavia.

Defence Secretary William Cohen ordered the deployment of another 176 planes to Europe, bringing to more than 800 the number of US aircraft available for use by Nato.

The US House of Representatives approved more than $13bn in extra funds for the Yugoslav campaign, twice the amount requested by President Clinton last month. The Senate has yet to vote on the spending commitment.

KLA rejects peace plan

The draft peace plan will provide for Kosovo refugees to return home

The Kosovo Liberation Army has rejected the draft peace plan agreed by Russia and the world's leading industrial countries on Thursday.

A spokesman for the Kosovo Albanian guerrilla force said several points in the agreement were "completely unacceptable".

He warned it was inconceivable that the KLA would agree to disarm after the events of the last few months.

The spokesman said the Balkans would be under threat as long as Yugoslav President Slobodan Milosevic remained in power.

He also said that moderate leader Ibrahim Rugova had no mandate to negotiate on behalf of the Kosovo Albanians.

Yugoslav silence on deal

Yugoslavia has not yet formally responded to the peace plan.

Belgrade's ambassador to the UN, Vladislav Jovanovic, said his country was still opposed to a foreign military presence.

The official Yugoslav news agency, Tanjug, said it was important that the UN Security Council adopt a resolution on a peaceful solution soon, but repeated that a key condition was an end to the Nato bombardment.

In another development, Yugoslavia has agreed to allow a team of UN humanitarian officials to visit Kosovo, after a request from the UN Secretary General, Kofi Annan.

The UN said an advance team of officials would leave for Belgrade in the next few days.

Peace plan delay

Further moves towards peace were held up when two delegates failed to attend a meeting in Bonn which had been intended to resolve details of a draft peace plan.

Nato and Russia agreed the plan on Thursday, but correspondents say big differences remain over the terms of the settlement.

Russian Foreign Minister Igor Ivanov said he was disappointed that Nato had not agreed to halt its bombardment of Yugoslavia.

So far, Russia and Nato have agreed on:

• the deployment of a UN-approved security presence to secure Kosovo after the withdrawal of Serb forces
• the return of refugees to their homes
• the establishment of an administration approved by the UN Security Council.

Disagreement remains over the role of Nato troops in the peace force.

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