An Ethiopian military helicopter crashed inside a United Nations peacekeeping force compound in the disputed Abyei region between Sudan and South Sudan, killing three crew members and injuring 10 passengers, the U.N. said in a statement Sunday.

The statement said the helicopter was carrying 23 passengers when it crashed on Saturday inside the compound of the U.N. Interim Security Force for Abyei (UNISFA), "killing three of its crew members."

"Ten passengers were injured with three in critical condition," it said.

The MI-8 helicopter was carrying Ethiopian troops from Kadugli in Sudan to Abyei, which has been contested since South Sudan gained independence in 2011.

"We are investigating the incident," said UNISFA's acting Head of Mission and Force Commander Major General Gebre Adhana Woldezgu.

Ethiopia is the sole troop contributing country to UNISFA, with some 4,500 soldiers on the ground.

The U.N. Security Council has warned that the situation in Abyei and along the Sudan-South Sudan border "continues to constitute a serious threat to international peace," and called on the two countries to show concrete progress on border demarcation and monitoring.

South Sudan seceded from Sudan in an acrimonious split following a 2011 referendum.

The two nations have disputes over several issues including the status of disputed oil-rich Abyei area and South Sudan's alleged support to Sudanese rebels.