The manoeuvres in the hills above Racak were carried out despite pleas for restraint from international monitors with the Organisation for Security and Co-operation in Europe (OSCE).
They also came on the day when Nato officials were meeting in Brussels amid calls for air strikes to punish Belgrade for the worst mass killing since the conflict in Kosovo flared in March last year.
Refugees were sent fleeing in terror from Racak as the security forces opened fire with heavy machine-guns, canon and mortars.
"They are shooting at our village," one man said as he ran, carrying a child in his arms. "Of course we're scared, just like they killed the others on Friday they would kill us today."
The Yugoslav authorities had informed the OSCE monitoring mission that they wanted to send their own team of forensic science experts to inspect the dead.
OSCE officials asked for and got a pull back of the rebel Kosovo Liberation army to allow the Serbian team to do their work.
In return, the OSCE officials demanded that the Serbian team should be unarmed and in plain clothes with no escort or show of force from the security forces.
But the hapless monitors had to watch helplessly as a steady build up of police and army units took place throughout yesterday morning.
The senior OSCE official, a British general, John Drewienkiewkz, was meeting Serbian officials when the police action began. "Our meeting broke up to the sound of gunfire," he said.
Later yesterday, Serb forces sealed off other villages in the area. Peace verifiers from the OSCE reported houses burning in villages west of Racak, 25 kilometres (15 miles) south of Pristina.
An OSCE official, Mike Philips, said international monitors reported heavy artillery and machine-gun fire in the area but it was unclear whether ethnic Albanians were resisting or the fire was coming exclusively from the government side.
In another area of Kosovo, Mr Philips said, Yugoslav tanks and armoured personnel carriers were moving into the area of Podujevo, 30 kilometres (18 miles) north of Pristina.
He said there were no reports of fighting near Podujevo, the scene of four days of clashes last month, but the government forces were "definitely in a position of intimidation".
The US State Department yesterday denounced Serb police efforts to enter Racak, calling them a "provocation".
"We condemn the further violence that has occurred this morning in the village of Racak in Kosovo, coming on the heels of the massacre of civilians in that village by Serb security forces," a spokesman said.
"The Serb return to the area was a provocation with the predictable result of instigating these clashes."Reuse content