Sri Lanka says it will now allow a team of United Nations investigators to visit the island, reversing an earlier refusal to grant them visas.
The panel was appointed in June by the UN Secretary General to look into reports of war crimes in the final stage of the conflict with Tamil Tiger rebels last year.
Sri Lanka opposed the move and set up its own internal commission.
Colombo now says the panel may visit and share evidence with its inquiry.
The foreign ministry said on Saturday they would be admitted so that they could make a presentation to the Sri Lankan commission. No date has been set.
Sri Lanka consistently denies its forces violated international humanitarian law during the long conflict, maintaining that only the Tamil Tigers did.
The BBC reports people suggesting otherwise are often labelled as traitors in Sri Lanka.
The UN estimates that up to 100,000 people were killed in the conflict.