Sri Lanka is planning an investigation into accusations of human rights abuses in the final stages of a 26-year civil war amid international frustration at the failure to look into numerous civilian deaths, a government spokesman said.

Former president Mahinda Rajapaksa, who was ousted in a surprise election defeat this month, had refused to cooperate with any UN investigation into claims the army committed atrocities in the war that ended in 2009.

Without some accountability for civilian deaths, the UN argues there will be no lasting reconciliation to allow Sri Lanka to move on, which dragged on for decades as ethnic Tamil rebels battled for autonomy in the north and east of the island.

“We are thinking of having our own inquiry acceptable to them to the international standards,” government spokesman Rajitha Seneviratne told a forum of foreign correspondents in Colombo on Wednesday. “It will be a new local inquiry. If we need, we will bring some foreign experts.”

In November, the UN high commissioner for human rights accused Rajapaksa’s government of trying to sabotage its own investigation and creating a “wall of fear” to prevent witnesses from giving evidence to its inquiry, which was set up in March.

About 40,000 Tamil civilians were killed in the final weeks of the war, most of them by the Sri Lankan army, the UN estimated in a 2011 report. Sri Lanka has rejected the accusations and has been conducting its own investigation.

The newly elected president, Maithripala Sirisena, in the runup to the vote promised a new investigation under an independent judiciary, but rejected demands for an international inquiry.

This week, he sent his senior adviser on foreign relations to meet UN officials to discuss the investigation, government sources said.

Seneviratne said the government was considering releasing political prisoners, mainly suspected members of the defeated Tamil Tiger rebel group.