NATO's nine-week-old bombing campaign against Yugoslavia reportedly took the lives of at least 27 civilians today when bombs and missiles hit a medical facility and senior citizens' home in the southern city of Surdulica and an apartment building in Novi Pazar.

In two days, more than 40 Serbian civilians have died in air raids.

NATO bombers also struck Yugoslav army positions in Kosovo in apparent support of the Kosovo Liberation Army (KLA), an ethnic Albanian rebel force that is trying to infiltrate Kosovo from neighboring Albania. Rebel fighters have made several attempts in recent days to enter the breakaway province, whose prewar population was 90 percent ethnic Albanian, but the Yugoslav army has turned them back.

NATO has stepped up bombing with the aim of forcing Yugoslav President Slobodan Milosevic to withdraw his troops and police from Kosovo, from which they have expelled more than 800,000 ethnic Albanians. The allies also want Milosevic to permit NATO to occupy Kosovo -- part of Serbia, Yugoslavia's dominant republic -- to ensure the return of the refugees.

With the increased bombing has come a recurrence of fatal blunders that, during the 69-day NATO campaign, have taken the lives of scores of civilians -- Serbs as well as ethnic Albanians. Attacks today and Sunday killed a total of 46 people, Serbian media reported.

In Surdulica, 220 miles southeast of Belgrade, the Yugoslav and Serbian capital, reporters saw 11 bodies lying under sheets near a medical complex and those of four elderly women on stretchers in front of the retirement home, which housed 35 people. A human hand protruded from the shattered building, and clothes hung limply from trees.

The blasts not only smashed a wing of the hospital, but also sheared and scorched the tops of tall pines. Yugoslav officials said at least four other victims were still buried in the rubble.

The attack, which took place shortly after midnight, was the second to hit civilians in Surdulica since the war began. On April 27, a missile hit a house there, and 16 people died in the explosion.

Later today, Yugoslav officials said missiles slammed into a residential area in the city of Novi Pazar. Ten people are reported to have died and at least 20 others were said to be wounded. Yugoslav officials said NATO apparently was aiming at army barracks. Since the war began, they generally have been vacated, but such structures apparently remain part of the "military machinery" NATO has pledged to destroy.

On Sunday, NATO jets attacked a bridge in central Serbia and reportedly killed 11 motorists crossing it.

In Brussels, NATO spokesmen said they knew nothing of civilian casualties. In the past, NATO has initially denied hitting civilians and, only a day or two later, acknowledged that bombs went astray.

NATO spokesman Jamie Shea said: "This alliance will not be shaken. We will not stop and we will not let up until Milosevic and his killing force withdraw from Kosovo."

The Yugoslavs argue that these errant attacks amount to war crimes.

"They violated basic international rules and all Geneva conventions. The Red Cross flag on the roof of the building was clearly visible," said Branislav Ristic, head of Surdulica's civil defense office.

The Reuters news agency reported from Morina, Albania:

Tensions were high along Kosovo's border with Albania after Yugoslav army shells destroyed a border post in Albania and more shells struck another village.

International monitors said Yugoslav shellfire destroyed the Albanian border post at Pogaj, just 500 yards from the main Morina crossing used by Kosovo refugees, as the KLA fought for control of high ground a few miles away.

Witnesses reported intense mortar fire at Mount Pastrik, which straddles the border, and at 7:20 p.m. five artillery shells apparently fired by Yugoslav forces crashed into Krume, a town about nine miles northwest of Morina and a slightly back from the frontier.

The Krume attack sent residents and international officials scrambling for cover. Police, soldiers and KLA fighters rushed to the scene.

A large force of Yugoslav tanks was reportedly approaching the border at another point where KLA guerrillas were active.