A Canadian scientist who has made a preliminary forensic examination of mass grave sites in northern Afghanistan is to urge the United Nations to launch a full-scale investigation. Professor Mark Skinner has concluded it is possible the graves are the result of atrocities. One of the anti-Taleban leaders, General Abdul Rashid Dostum, has claimed thousands of people were executed at night in the desert by a rival northern anti-Taleban commander General Abdul Malik. General Dostum says many of the victims were Taleban fighters who had been taken captive in the north. But General Malik denies being linked to any killings. Our correspondent Alan Johnston sent this report.

The news that mass graves had been discovered in northern Afghanistan broke a month ago. The United Nations contracted a forensic anthropologist, Professor Mark Skinner, to make a preliminary examination of the sites.

He has completed his work and has concluded it is possible there were indeed mass executions. Prof Skinner says he will urge the UN to launch a thorough investigation, drawing on the expertise of a range of international experts.

The inquiry is expected to focus on several water wells used by shepherds in the desert west of the town of Shebergan.

Taleban troops held in Shebergan jail are alleged to have been thrown down the wells. Grenades were reportedly thrown after them and the shafts were then bulldozed over.

Prof Skinner, who found fragments of human skull around one of the shafts, says the wells should be opened by a UN team and their contents examined.

He will also urge an investigation of mass graves at another site near the river port of Heyratan.

Prof Skinner saw corpses there which had their arms tied behind their backs. He said it is quite likely they were executed.

The mass graves were brought to international attention by one of northern Afghanistan's anti-Taleban commanders, General Dostum, an ethnic Uzbek.

He says the killings went on while he was in exile earlier this year. He blames them on his rival, General Abdul Malik, another anti-Taleban commander.