Tension has increased between Serbia and Montenegro, its junior partner in federal Yugoslavia, amid reports that Yugoslav troops have closed Montenegro's border with Croatia.

At the same time, neighbouring Croatia says that Yugoslav soldiers have entered a disputed strip of land on its border with Montenegro.

And on Yugoslavia's joint border with Albania, a clash between the two countries' armies, was reported, with one Albanian soldier injured.

Meanwhile a new refugee crisis is building up on Macedonia's border, as the government there refuses to allow the latest exodus from Kosovo to enter the country.

Strikes

Nato began its fifth week of air strikes against Yugoslavia by launching at least three missiles at the 24-storey building in New Belgrade which housed offices belonging to President Milosevic's Socialist Party of Serbia.

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It was also home to the Yugoslav Left Party led by the president's wife, Mira Markovic, and to radio television channels, including a radio station run by Mr Milosevic's daughter.

Nato spokesman Jamie Shea described the building as "a high-value target at the very centre of the power structure in Belgrade".

Dr Shea said the building was the centre of the Yugoslav propoganda machine, and an important link in the defence communication network.

Witnesses said a huge fire raged through the building. Officials from the ruling party say people were still working inside when the missiles struck but there was no word on casualties.

(Click here for a map showing latest strikes)

Serb TV showed the bridge under attack

Yugoslav media also reported Nato strikes on northern and central Serbia, including the last remaining bridge over the Danube in the town of Novi Sad. An oil refinery there was also reported hit, as was a TV transmission tower outside the city.

Among other reported targets were an ammunition factory in Valjevo and a military and civilian airport in Ponikve in central Serbia.

Border closed

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The latest onslaught came as Yugoslav troops were reported to have closed Montenegro's border with Croatia, and Belgrade military authorities were demanding control of the republic's police force.

Police at local border crossings have been allowing Westerners, including journalists, into Montenegro without Yugoslav visas - actions regarded by the army as part of a pattern of disloyalty on the part of Montenegro.

Montenegro's President Milo Djukanovic was on Wednesday reported as saying that his government had received a letter from federal army headquarters ordering that the army take control of the republic's police.

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"It is out of the question that the Ministry of the Interior could be subordinated to the Yugoslav army," he said in the London Financial Times.

There were other signs of the conflict spreading into Montenegro with reports from Nato officials that Yugoslav security forces had attacked three ethnic Albanian villages inside Montenegro, killing six people.

Disputed zone

Neighbouring Croatia has complained to the United Nations that several hundred Yugoslav soldiers have entered a demilitarised zone on its border with Montenegro. The Prevlaka peninsula controls access to an important Yugoslav naval base in Montenegro.

Croatia's UN ambassador, Ivan Simonovic, told the Security Council that up to 300 Yugoslav soldiers had moved into the zone, and demanded their immediate withdrawal.

Both Croatia and Yugoslavia claim the zone as their own.

Macedonia added its voice to growing discontent in the region, with President Kiro Gligorov describing the continuing influx of Kosovo Albanians fleeing Yugoslav security forces as the greatest threat to Macedonian security since independence in 1991.

Mr Gligorov said the country's interest was to preserve internal stability and external security. The United Nations refugee agency, the UNHCR, says it has been denied access several times over the last two days to refugees arriving at the Macedonian border.

It has appealed to western governments to take Kosovo Albanian refugees away from Macedonia as relief camps there are full.

Shoot-out

Along other tense borders, Yugoslav and Albanian troops near the Qafa e Prushit border post exchanged fire for over six hours in the first clash between the two armies since the start of the Kosovo conflict.

The Kosovo Liberation Army is known to be active along the border, trying to infiltrate its fighters into Kosovo. Last week the Albanians complained that Serb forces had crossed the frontier, burnt down a village and occupied a border post before withdrawing. Belgrade denied any such incursion.

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