The United Nations says three Ethiopian peacekeepers died while Sudan refused to allow them to be flown to a hospital.

U.N. peacekeeping chief Alain Le Roi told reporters Thursday the peacekeepers were taken to a helicopter after being seriously wounded in a land mine explosion. But he said the helicopter waited for three hours because the Sudanese government threatened to shoot it down if it took off.

A U.N. spokesperson says Secretary General Ban Ki-moon had taken the issue to Sudan's ambassador to the U.N. The spokesperson said Mr. Ban stressed that any delay is “unacceptable” when it comes to saving lives.

The three Ethiopian peacekeepers were wounded Tuesday in a blast while on patrol in the disputed Abyei region. A fourth peacekeeper died instantly in the explosion. Seven others were wounded but survived.

Ethiopia provided the troops for the recently-approved Abyei peacekeeping force.

Abyei sits on the border between Sudan and the new nation of South Sudan. The two countries have been unable to decide which one should control the oil-rich region.

Sudanese troops occupied Abyei on May 21, about seven weeks before South Sudan declared independence.

Both sides have agreed to withdraw their forces under a deal that led to the creation of the U.N. peacekeeping force.