Soviet and Afghan troops shelled both ends of a major tunnel north of Afghanistan's capital in raids that killed hundreds of civilians, Western diplomats said Thursday.

The diplomats, who demanded anonymity, quoted reports from Kabul as saying that "after bombing of north and south ends of Salang tunnel, Soviet and Afghan artillery obliterated all dwellings and villages south of the tunnel."They quoted Afghan sources, including an eyewitnesss report, as saying the raids occurred Monday at the Salang tunnel on the main highway, which connects Afghanistan and the Soviet Union.

"Soviet forces and Afghan Special Guard committed a major atrocity in Salang area on Monday," the diplomats said. "Reportedly, hundreds of civilians were killed."

"According to eyewitnesses, no dwellings remain," they said.

A dispatch received from Western diplomats in Kabul said witnesses reported seeing "Soviet tanks rolling over dead bodies of victims of Salang road."

The dispatch said the account of destruction of all dwellings came from three separate sources, including one diplomat who is an outspoken defender of Afghan President Najib.

Also Thursday, Afghanistan's state-run Radio Kabul said 206 guerrillas were killed in two days of fighting in the eastern province of Parwan. It said 109 more rebels were killed in Kandahar Thursday.

The report came the same day Moslem insurgents said they had stepped up attacks on Kandahar, Afghanistan's second-largest city, because the Soviets were airlifting tons of arms and ammunition to prop up government forces there.