An Afghan official with close ties to President Najibullah charged Tuesday that Pakistani troops supported by tanks, rocket launchers and artillery led the attack that caused the fall of the strategic eastern city of Khost.

Ahmad Sarwar, Afghanistan's ambassador to India, charged at a news conference that Pakistani troops crossed the border into Afghanistan and led the Afghan Mujahideen rebels in attacking Khost, 100 miles southeast of the capital of Kabul."The Mujahideen never discuss their operations inside Afghanistan with us. No Pakistani troops took part in the Khost offensive and there was no Pakistani military adviser on the Khost front," a Foreign Office spokesman in Islamabad said Monday.

Afghan President Najibullah announced on state-run Radio Kabul Monday night that all contact had been lost with Khost, which sits astride a highway from the border. He declared Tuesday a day of mourning for those killed in the battle.

The Mujahideen rebels said Sunday they had captured Khost, which had a garrison of about 1,500 troops. The capture of the staunchly pro-communist town was of symbolic importance to the Muslim fundamentalist rebels.

The Afghan ambassador, who is married to the sister of Najibullah's wife, said Pakistani forces using tanks, artillery and rockets attacked Khost from four sides Sunday and the battle continued until Monday.

He said the attack on Khost caused a large number of civilian casualties among the city's 50,000 people and that the city was "looted and robbed" by the Pakistani military.