(Adds comment from second rebel group, quotes, detail)
KHARTOUM, Jan 8 (Reuters) - Darfur rebels accused Sudan's army of bombing their positions on Thursday, breaking a period of relative calm in the country's violent west.
No one was immediately available to comment from Sudan's armed forces.
The insurgent Justice and Equality Movement (JEM) told Reuters government helicopters and Antonov planes attacked their fighters across a wide area of north Darfur from around midday on Wednesday until late Thursday afternoon.
"There is bombing going on right now," said JEM commander Suleiman Sandal at 2pm local time (1100 GMT) on Thursday.
"They have seen JEM forces moving across the area. They think JEM is going to attack them ... This is the first for some time."
The reports were confirmed by Ibrahim al-Helwu from the branch of the rebel Sudan Liberation Army (SLA) controlled by Abdel Wahed Mohamed Ahmed al-Nur.
International sources, who asked not to be named, said they had heard similar reports.
"They are bombing randomly in a very large area. Large areas of grassland are on fire," said al-Helwu. He added a number of civilians had been injured, but had no figures.
The attacks were on territory around at least nine settlements including the towns of Kutum, Birdik, Mallit and Um Sidir, the rebels said. Sudan's president announced an "unconditional" ceasefire in the region less than two months ago.
The joint United Nations/African Union UNAMID peacekeeping force said it was looking into reports of clashes between government and rebel forces in the days after the November ceasefire announcement. But the fighting appeared to die down in December.
JEM's accusation will add to tension mounting ahead of a ruling from the International Criminal Court on whether to issue an arrest warrant against Sudanese President Omar Hassan al-Bashir on charges of orchestrating genocide in Darfur.
A senior foreign office official on Monday told Reuters the government had intelligence JEM was planning to attack Sudanese cities and oil fields as soon as the court's decision was announced.
Sandal confirmed JEM was planning to mark the ruling with some form of action, but declined to go into details.
"It is true we are preparing for the ICC day. But we are not sure what day it will be," he told Reuters, speaking by satellite phone from Darfur.
"We are preparing militarily and with the IDP (internally displaced people) camps. There will be demonstrations. We are trying to make it an important day for justice."
Mostly non-Arab rebels took up arms in early 2003 accusing Khartoum of neglect. Khartoum mobilised militias to quell the revolt, who now stand accused of war crimes.
An estimated 200,000 people have died in the violence and 2.5 million have fled their homes. Khartoum accuses the western media of exaggerating the death toll.
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