KHARTOUM  - Thirteen Sudanese military personnel died and nine others were injured when their transport plane crashed west of Khartoum Sunday on its way to conflict-plagued Darfur, state media reported.

"Thirteen were killed instantly, and nine were taken to hospital," Sawarmi Khaled Saad, the Sudanese army spokesman, was quoted as saying by the state SUNA news agency. It is the worst toll in a series of Sudanese military aviation incidents since early last year, and follows a recent surge of unrest in Darfur, the far-west region where a rebellion began nearly a decade ago.

Saad said the plane carried six crew and 16 other members of the armed forces.

"The pilot informed the airport that he had a problem with one of his engines," before the plane went down in the desert west of Jebel Aulia, Saad told AFP earlier.

Saad added that the Antonov was carrying military equipment from Khartoum to El Fasher, the capital of North Darfur state.

A witness said a helicopter ferried the dead and injured from the crash scene, which had been sealed off by soldiers, about 70 kilometres west of the capital.

Jebel Aulia is a popular recreational site about one hour's drive south of the Khartoum area.

Sudan's armed forces, which rely on Russian-made planes and helicopters, have experienced a number of aircraft losses in recent years.

In July, Darfur rebels said they shot down an Mi17 helicopter, killing seven personnel from the military which blamed a malfunction for the incident.

Last December, all six crewmen aboard another military helicopter died when it crash-landed and burned in North Kordofan state. The army blamed a technical problem, as it did in April last year when a helicopter went down in Darfur killing all five soldiers aboard.

The United States on Thursday voiced concern that security in western Darfur was worsening and threatening the implementation of peace accords there.

"The United States is deeply concerned by the sharp deterioration in security in North Darfur and adjacent parts of Jebel Marra, Sudan," State Department spokeswoman Victoria Nuland said in a statement.

More than 70 civilians were killed in Hashaba, north Darfur, between September 25 and 27 in fighting and aerial bombardments between rebels and the Sudanese government forces, she said.

The US was also "appalled" by Tuesday's attack on a UN patrol in which four Nigerian peacekeepers were killed and eight injured, she added.

Rebels from black African tribes rose up against the Arab-dominated Khartoum government in 2003. Clashes with government troops, banditry and inter-ethnic fighting continue, but the levels of violence have fallen compared to nearly a decade ago.