The human rights group, Amnesty International, says it won't send an expert to help excavate a suspected mass grave in northern Sri Lanka without guarantees of co-operation and security from the government.

A spokesman said the assurances had been sought for some time without success.

Sri Lanka'sAttorney General said earlier that he had invited Amnesty International toparticipate when conditions returned to normal in the area.

The BBC Colombo correspondent says the Attorney General's statement will be seen by many as a delaying tactic.