BELGRADE, Yugoslavia (AP) _ NATO planes launched another round of airstrikes against Yugoslavia today, and the alliance confirmed that allied aircraft struck two convoys in Kosovo _ one military and one mixed of military and civilians.

At NATO headquarters in Brussels, a military officer speaking on condition of anonymity said today that evidence pointed to an allied plane having struck at a mixed convoy of refugees and Serb military vehicles Wednesday in western Kosovo.

In the strike, what appeared to be a tractor was hit, the officer said. In the long column of refugees, tractors were towing flatbed trailers packed with dozens of refugees.

Yugoslav officials said the convoy attack, which it said killed 64 people and wounded 20, came from NATO warplanes. Previously, the alliance acknowledged attacking only military vehicles and said there were indications that Serbs themselves had attacked refugees, either from the ground or the air.

Nearly 24 hours later, the circumstances remained murky. An international observer, part of a team monitoring the Albanian border, said today that refugee accounts indicated that Serbs, using MiG fighter jets and helicopters, had taken advantage of a NATO military strike to deliberately target refugees.

``The Serbs can't get at NATO directly, so they are taking it out on the refugees and making NATO look bad,'' said Pjarke Tharkildsen, a Danish military officer with the Organization for Security and Cooperation in Europe, which watches the frontier.

The convoy's movement came against a backdrop of what is described by Western officials as a vast campaign of ``ethnic cleansing'' in which Serbs have systematically driven more than half a million ethnic Albanians out of Kosovo. That exodus is now gathering new force again after ebbing in the past week.

Thousands of refugees poured across the Albanian border at the Morini crossing between midnight and dawn today, some of them witnesses to the carnage of the convoy attack. Shaban Hasanaj, 15, came along later in a column of thousands that fled toward the Albanian border on foot, and said he saw the aftermath of the strike.

``I could see bodies without heads, tangled arms and legs,'' he said.

Early today, what was apparently Serb artillery fire landed inside Albania just beyond the border post. No casualties were reported, but the shells hit in an area where humanitarian workers have been operating and near where refugees have been passing.

Wednesday's bloodshed along a rural road near Djakovica (pronounced jah-koh-VEET'-sah) marked the latest grim drama in a 3-week-old air war that has seen NATO warplanes hammer Serb targets throughout Yugoslavia in an effort to force Yugoslav President Slobodan Milosevic to accept a peace deal for Kosovo.

In the latest wave of attacks, NATO targeted military barracks, transmitters carrying state-run TV and a series of bridges. The state-run Tanjug news agency said 10 towns or their wider areas were targeted overnight.

New NATO strikes were also reported in and around Kosovo, continuing into daylight today.

At around 11 a.m., three strong detonations were heard just southeast of the Kosovo capital, Pristina, Tanjug said. Air raid alerts sounded in the city.

Also this morning, two missiles targeted the village of Lukare, northeast of Pristina, Tanjug said. The airport at Slatina, pounded by a wave of strikes all week, was hit again, it said.

Huge refugee columns like the one hit could signal a final push by Serb forces to rid the disputed province of its ethnic Albanian majority.

Macedonia took in 3,000 more Albanians Wednesday and officials with the U.N. refugee agency said the numbers could swell to 50,000 based on refugee reports that Serbs are clearing out the region around Urosevac, 20 miles from the border.

More than 3,000 Kosovar Albanians crossed into northern Albania late Wednesday and early today. Many said they had been walking for three days and nights before finally reaching the relative safety of the border.

The convoy attack's aftermath _ as seen in video shot under Serb supervision _ was horrific. Bodies and belongings were scattered along a rural-looking roadway, and the smashed wreckage of vehicles was visible. People in rough peasant clothing, some with blood streaming down their faces, loaded bodies of the dead and wounded into cars or wheelbarrows.

In Washington, Pentagon spokesman Kenneth Bacon said Gen. Wesley Clark, the top NATO commander in Europe, said he had reports that after military vehicles in the refugee convoy were hit, Serb ``military people got out and ... began to attack civilians'' in a nearby convoy on the same road.

According to Bacon, Clark believed a military convoy hit by NATO was traveling separately but ``in close proximity'' to the refugee convoy that Clark has accused the Serbs of attacking in retaliation.

Bacon also said there was another reported attack against refugees. U.N. officials quoted refugees as saying that 600 women and children were attacked by Serb aircraft while traveling Wednesday on a road between the Kosovo town of Prizren and Kukes, Albania, according to Bacon. He said there was no word of casualties.

In Belgrade, Yugoslav Foreign Ministry spokesman Nebojsa Vujovic said Yugoslavia had no planes in the air and denounced the strike as a ``crime against humanity.''

According to Serb accounts, two separate refugee convoys were bombed, most of them made up of women, children and elderly ethnic Albanians traveling by tractors, trailers, in private cars or on foot.

If the reported death toll were accurate, it would mark by far the largest single loss of civilian life in an airstrike during the Yugoslav-NATO standoff.

NATO has said repeatedly it held Milosevic responsible for the safety of ethnic Albanians driven from their homes in Kosovo but unable to leave the province.