Newsweek magazine says the Joint Chiefs of Staff wrote to Defence Secretary William Cohen some weeks ago saying that ground troops must be committed to "guarantee fulfilment of the administration's political objectives".

Military planners say time is running out for a decision if the Kosovo-Albanian refugees are to return to their homes before winter.

"A ground war would have to commence by the beginning of August, and the forces required must start assembling by the beginning of June," the magazine quoted Pentagon sources as saying, in its Monday edition.

The report - which has not been confirmed by the Pentagon - was published as America's former military chief Colin Powell criticised the conduct of the war in Yugoslavia.

General Powell: "Go all out"

General Powell - who led United States forces during the Gulf War - told American television that the exclusive use of air power had given Yugoslav President Slobodan Milosevic the decision as to when the Kosovo conflict would be ended.

"Go all out ... war involves casualties," he said, echoing complaints by many military strategists that an air operation will never be enough to force President Milosevic to back down.

BBC's Mark Laity explains Nato's strategy since the latest civilian killings

Defence Secretary Cohen responded by saying that Nato was going all out with its air campaign. Washington, however, remains determined not to send in ground troops to fight a war.

Exactly how and when troops might enter Kosovo will be discussed when UK Foreign Secretary, Robin Cook, visits the United States later this week.

British officials have denied reports that they are frustrated by the Clinton administration's refusal to commit ground troops to the conflict.

Bombing 'is working'

Nato chief Javier Solana said the bombing campaign was working and they would stick with it.

Jane Bennett-Powell: "Nato keeps up the pressure on Serbia"

He told the BBC he wanted Kosovo Albanian refugees to return this year.

"It is our wish, and we are doing our best so they can return home as soon as possible, in any case before the winter."

In a joint editorial in Sunday's Washington Post, Robin Cook and the US Secretary of State, Madeleine Albright, said the "brutality" of President Milosevic made them more determined than ever to continue the attacks.

And in the wake of the bombing of the village of Korisa in which more than 80 civilians were reported killed, they also warned that more civilian casualties could result from the Nato campaign as "perfection is unattainable".

Mike Williams in Belgrade: Hopes of peace moves within a week

On the 55th night of bombing, Nato said its operations against Yugoslavia had been limited by poor weather to targets around south-west Kosovo. It said its planes had attacked some Serbian artillery and military vehicles.

Explosions were heard around Belgrade and the Serbian towns of Cacak, Kraljevo and Uzice. Two explosions were also reported in the Kosovo capital, Pristina.

Heavy anti-aircraft fire was reported throughout the country. Over Belgrade, the guns were said by local sources to have fired at a number of reconnaissance drones which flew over the city in the early hours.

(Click here to see a map of the most recent Nato strikes)

The search for a diplomatic solution to the Kosovo crisis turns on Monday to Brussels, where European Union foreign ministers meet their Russian counterpart and the Kosovo Albanian political leader, Ibrahim Rugova.

David Shukman: Chance to get EU-Russian relations back on track

Ministers will discuss a German plan to bring long term stability to the Balkans, once the conflict is over.

BBC Europe correspondent David Shukman says the meeting will be a chance to get relations with Russia back on track after the bombing of the Chinese embassy in Belgrade earlier this month.

Apache deployment puzzle

Nato officials have been forced into denials that the Pentagon is refusing to allow the deployment of its 'tank-busting' Apache helicopters in Kosovo for fear of taking casualties.

Two Apaches have crashed during training in Albania

The fleet of 24 Apache AH-64s was declared ready for use last week after training in Albania, but has not yet gone into action.

Nato's military commander Wesley Clark is reported to have been refused permission to use them, but spokesman Jamie Shea said he was "not aware" of any disagreement on the issue.

Meanwhile, speculation is growing that two Serb Army soldiers held as prisoners of war are about to be released by the US military.

Pentagon officials, speaking on condition of anonymity, said the men - captured by the Kosovo Liberation Army and handed over to the US - may be set free as soon as Monday. They are being held in Germany.

After President Milosevic agreed earlier this month to free three American soldiers captured on the Kosovo-Macedonia border, President Clinton said the release of the two Serbs was under consideration.

UN monitors arrive

A UN team heading for Kosovo arrived in Belgrade on Sunday for the first part of its humanitarian mission to Yugoslavia.

The mission is made up of 16 people from the UN's main agencies as well as the British Save the Children Fund.

The team has been assured access to some of the towns where refugees have spoken of systematic ethnic cleansing. It will be escorted by Yugoslav police.

BBC News' Orla Guerin meets refugees in Macedonia

Several hundred refugees from Kosovo who arrived in Macedonia over the weekend say many of them were forced to leave because Serb forces would not allow them to buy food in the shops.

One woman told UN officials that her father had gone out to buy food and had later been found shot dead.

The groups arriving over the past two days were the first refugees to arrive in Macedonia since the government temporarily closed the border ten days ago saying it could not cope with a mass influx.

• Serbs blamed for Nato killings
• Refugees say Serbs withhold food
• Embassy blame shifts to map agency
• Nato dumps bombs in Adriatic
• Blair on Balkan solidarity mission

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