Sri Lanka is trying to sabotage a United Nations human rights inquiry into war crimes in the Southeast Asian country during the decades-long civil war between the Sri Lankan army and the Tamil rebels, a U.N. spokesman said Friday. Witnesses were allegedly intimidated and Sri Lankan officials aren't cooperating with the probe, Reuters reported.

"Sri Lanka's government has refused point blank to cooperate with the investigation,” U.N. human rights spokesman Rupert Colville said during a U.N. briefing Friday in Geneva, according to Reuters. He said the pushback from Sri Lanka “raises questions about the integrity of the government. Why would a government sabotage an independent investigation?"

The U.N. is trying to investigate whether the Sri Lankan government and the Tamil rebels engaged in war crimes during the two sides’ decades-long civil war, which ended in 2009 with the Sri Lankan government reclaiming territory held by the Tamils in north and eastern Sri Lanka.

The war crimes inquiry isn’t the only gripe the U.N. has with the Sri Lankan government. Last week, the body’s human rights panel also slammed a Sri Lankan constitutional amendment that the U.N. said gives Sri Lankan President Mahinda Rajapaksa too much power, the New York Times reported.

Sri Lanka’s 18th amendment “empowers the president to dismiss or appoint members of the judiciary and other independent bodies,” the U.N. said in a report released last week.  Rajapaksa used the amendment to fire Sri Lanka’s chief justice earlier this year.

Sri Lanka said the U.N. claims were without merit and accused the U.N. human rights panel of bias. Sri Lanka Information Minister Keheliya Rambukwella said the U.N. didn’t take into account civil and political threats from the Tamil opposition, whom he said killed 700 Sri Lankan police officers at the height of the civil war in 1990.

“That shows very clearly how biased they are,” Rambukwella said. “There were 700 policemen who were killed, blindfolded after being asked to surrender. Have they mentioned about that? I can mention 101 cases like that.”