KHARTOUM (Reuters) - One aid worker was killed and three others wounded when a grenade hit their office during a gunfight between competing security forces on Thursday in the biggest city of Sudan's Darfur region, the United Nations and witnesses said.
Clashes between the army, rebels and rival tribes have surged in the vast and mostly lawless region in recent months, but had until now been confined to rural areas.
Residents said heavy gunfire could be heard for hours near the security headquarters in Nyala, the capital of South Darfur state and the second-biggest city in Sudan. Men dressed in military uniform were seen exchanging fire with people inside the security compound.
A Sudanese aid staff person working for an international organisation was killed and three colleagues were wounded when a rocket-propelled grenade hit an office in crossfire, the U.N. said in a statement, without naming the employer. Two of them were treated with critical wounds in a hospital.
"There are also reports that some offices and premises of international organisations in Nyala were looted today," the United Nations said in a statement.
State authorities blamed "actions between the security forces", according to a statement, which gave no details. The government imposed a night curfew in Nyala.
"People are panicking and shops are closed," another resident told Reuters by phone as gunfire resounded in the background.
The United Nations said it had cancelled a regular flight from Khartoum to Nyala for security reasons, and U.N. staff in the city were moved to a bunker. By nightfall they were still waiting to be evacuated to a safer U.N. base, a U.N source said.
In separate violence, three Nigerian peacekeepers were wounded when unknown assailants ambushed them with rocket-propelled grenades on their way to Nyala on Wednesday, the UNAMID spokesman said.
At least one of the assailants was also killed, he said.
Law and order have broken down in most parts of Darfur since mainly African tribes took up arms in 2003 against Sudan's Arab-led government, which they accuse of discriminating against them. Khartoum denies this.
Violence is down from its peak in 2004-5, but has picked up again this year, involving the army, rebels and Arab tribes, many of which were armed by the government early in the conflict and are now fighting among themselves over resources and land.
In April, a group of reserve policemen staged a brief mutiny in El Geneina in West Darfur state.
Events in Darfur are difficult to verify because Sudan severely restricts access to foreign journalists.
The International Criminal Court has indicted President Omar Hassan al-Bashir and other Sudanese officials for masterminding war crimes in Darfur. Sudan has dismissed the charges as political campaign against the African country.
Reporting by Khalid Abdelaziz and Ulf Laessing; Editing by Mark Trevelyan and Michael Roddy