Darfur rebels and Sudan's army fought heavy battles in the North Kordofan province near Khartoum on Saturday, a local government official and witnesses said.

The Darfur Justice and Equality Movement (JEM) said it was strengthening its forces in Kordofan but not attacking government troops - to avoid causing civilian casualties.

But a local government official said the heavily armed rebels had scattered after an army counter-attack.

Sudan tightened security in the Sudanese capital late on Thursday because of the fighting and the army accused Chad on Saturday of backing the rebels, whose latest attack is the closest they have come to Khartoum.

Diplomatic missions hunkered down after warnings from the Sudanese foreign ministry, although life in the capital for most Sudanese seemed to continue as normal.

"The government and the armed Darfur movements are engaged in battles and there was bombing by planes and the rebels have scattered," Abdel Majid Abdel Farid, a member of the administrative council of North Kordofan's eastern town of Hamrat al-Wizz told Reuters from the area.

He said the Darfur rebels on Friday had spread out all over the state in an "unprecedented manner" carrying very heavy weapons.

The reports of bombing came from civilians north of his town, he added: "The civilians here are very, very scared."

It was difficult to obtain civilian casualties figures in the area as fighting was continuing, he said, and the JEM said it was tightening its control on Kordofan.

"We are deploying our forces as and when we see fit to," said senior JEM official al-Tahir al-Feki. "We are making a total deployment and getting a grip on Kordofan" he added.

"But we are not engaging in any activities that would result in displacing civilians."

The army told the state news agency SUNA in a statement it had repulsed an attack from the Chadian army which used heavy artillery in the Chad-Darfur area of KashKash late on Friday.

"The Chadian army attack came as direct support for the sabotage attempt by (JEM leader) Khalil Ibrahim which the armed forces discovered and brought under control," SUNA quoted the armed forces spokesman as saying.

Darfur's JEM have attacked government forces in Kordofan in the past but in hit-and-run raids but this is the closest they have come to the capital.

International experts estimate some 200,000 people have died and 2.5 million killed in five years of fighting in Darfur after mostly non-Arab rebels took up arms accusing central government of neglect.

The International Criminal Court has issued arrest warrants for a junior government minister and an allied militia leader accused of war crimes. Khartoum refuses to hand them over and blames the Western media for exaggerating the conflict.