Ombudsman Nurdi Nukhazhiyev said a group of residents told him last week about the suspected mass grave, at an asphalt plant about 25 kilometers from Grozny.
He said it contained the bodies of men, women and children who were killed on Oct. 30, 1999, when their column of vehicles came under fire from federal troops.
The Defense Ministry had no immediate comment. In the past, the military has denied systematic abuses during the fighting in Chechnya but said insurgents routinely used civilians as cover.
"All the vehicles [in the convoy] were carrying white flags made out of bed sheets so the troops would not shoot," Nukhazhiyev said Tuesday, addressing a conference on missing persons organized by Chechnya's government.
He said they were refugees trying to reach another part of the region to escape fighting.
"However, as soon as the column came over the brow of the hill ?€¦ the federal forces opened fire," he said. "After completely destroying the convoy of refugees, the soldiers buried the corpses together with their vehicles and belongings in a big pit on the territory of the asphalt plant, which is located near the road."
He said witness accounts suggest that 250 to 300 people were buried at the site. Human rights groups and the media reported the attack on the convoy at the time.
Nukhazhiyev said he wanted the remains at the site to be subjected to forensic tests to establish their identity.
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