A Libyan military spokesman quoted by The A.P., Ahmed Omar Bani, said that the attack occurred Saturday but that the Qaddafi loyalists had crossed the border several days earlier.

Separately, officials of the provisional government said Sunday that they had discovered the site of a mass grave in Tripoli with the remains of more than 1,200 prisoners who were massacred in 1996 at Abu Salim prison.

The officials said they located the grave, in a weed-filled lot behind the prison, after interrogating former security guards who had worked there. The field has not yet been excavated.

During a visit to the site on Sunday, there was no way to tell with certainty whether it contained human remains. Someone had collected dozens of bones, including many that appeared to belong to animals. Soldiers showed reporters what appeared to be a human jaw, but they could not say where it was found. Other bones and bits of clothing were scattered across the field.