Sri Lanka's government says it will now allow a team of UN investigators to visit the island, reversing an earlier refusal to grant visas.
The three-man panel was appointed in June by the UN secretary general to look into alleged war crimes in the final stage of the government's war with Tamil Tiger rebels in 2009.
Sri Lanka angrily opposed the move and set up its own internal commission.
Colombo now says the panel may visit and share evidence with its inquiry.
Sri Lanka consistently denies its forces violated international humanitarian law during the long conflict, maintaining that only the Tamil Tigers did.
People suggesting otherwise are often labelled as traitors in Sri Lanka.
The fact that Colombo has changed its mind and will now admit to the country the panel is something of a concession, says the BBC's Charles Haviland, in Sri Lanka. BBC News
