Updated

A U.N. peacekeeper from Sierra Leone was killed and another seriously wounded when their vehicle was attacked by gunmen in the Darfur region of Sudan on Friday, the United Nations said.

The attack took place in Duma village, 23 miles (37 kilometers) northeast of the town of Nyala, when four gunmen opened fire on the vehicle carrying five soldiers serving with the joint U.N.-African Union force in Darfur, the U.N. said.

Earlier this week, four Ethiopian peacekeepers deploying to Sudan's contested Abyei region died in a land mine explosion, three of them after Sudan refused requests to let them be flown out of the region for medical care, according to U.N. officials.

The peacekeeper injured Friday, also from Sierra Leone, was transferred to a hospital where he underwent surgery, the U.N.-AU force known as UNAMID said in a statement.

"The attack on our peacekeepers is deplorable and our hearts go out to the families and friends of the deceased," said UNAMID deputy representative Aichatou Mindaoudou Souleymane. "UNAMID is doing all it can to render treatment to the injured, and, with the Sudanese police, to find the perpetrators and bring them to justice,"

The U.N. Security Council in late June authorized a 4,200-strong Ethiopian peacekeeping force to deploy for six months in the contested region of Abyei, which lies between Sudan and the new nation of South Sudan. The U.N. troops are to support an agreement between the two governments that calls for demilitarizing the contested border region near major oil fields that both the north and south claim.

The Ethiopian troops began deploying last month and Le Roy, said about 1,200 are on the ground.

U.S. Secretary of State Hillary Clinton expressed alarm Friday at reports that the Sudanese government denied flight clearance for the medical evacuation of the Ethiopians, saying "three wounded soldiers died during this unnecessary delay."

"The United States ... strongly condemns the government of Sudan's non-compliance with its obligation and its obstruction of the work of the United Nations," she said in a statement.

"This tragic incident also underscores the importance of establishing peace and security in Abyei, and between Sudan and South Sudan," Clinton said.