The site in the eastern coastal town of Kalavanchikudy has been under investigation since a resident petitioned the local court, claiming the remains of around 100 Muslims killed 24 years ago at the height of Sri Lanka's ethnic war were buried there.
The claims of a mass grave in the east of the island follow the discovery of several similar sites elsewhere in the island's war zone as well as in the central part of the country.
"There were difficulties in getting forensic experts from Colombo," said the official in Kalavanchikudy, 330 kilometres (206 miles) east of Colombo by road.
"The excavation was rescheduled for November 24."
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He said it was the second time the excavation, initially scheduled to start on July 1, had been delayed for that reason.
Rights groups have accused Sri Lankan authorities of failing to investigate what the UN calls credible allegations of war crimes by both sides.
Some of the Tamil guerrilla leaders linked to atrocities have defected to the government since the conflict ended, and there have been allegations that the authorities were trying to protect them.