The United States says it won't block Russia's attempts to establish a U.N. tribunal to investigate allegations that Kosovo's ethnic Albanian wartime leaders killed hundreds of Serbs civilians after the country's lawmakers rejected amendments to the constitution to allow a Western-backed court deal with the claims.

The U.S. Embassy in Kosovo said in a statement on Saturday it was "deeply disappointed" by Friday's vote.

A 2010 Council of Europe report claimed former rebel leader turned politician Hashim Thaci and other Kosovo guerrillas ran a criminal ring in 1999 and that some victims were allegedly killed for their organs to be sold on the black market.

The 120-seat legislature voted 75-7 on Friday in favor of the amendments, but failed to secure a two-thirds majority to approve the changes.