Rebels in Sudan's Darfur region said on Monday they had captured 52 international peacekeepers, most of them from Senegal, and accused them of cooperating with the country's security service.

The joint U.N./African Union UNAMID peacekeeping force has been repeatedly caught in the crossfire during almost 10 years of fighting between government troops and insurgents in Sudan's remote west.

But the capture of more than 50 soldiers will be seen as a major setback for an already stretched mission, set up to keep the peace in a territory the size of France.

We are holding the UNAMID soldiers because they entered our territory without permission and because they were accompanied by three Sudanese we suspect work for the security services, Gibreel Adam Bilal, a spokesman for the rebel Justice and Equality Movement (JEM), told Reuters.

Bilal said JEM fighters had stopped the soldiers late on Sunday in Shagied Karo in north-western Darfur. JEM suspected UNAMID of helping Sudan's security services spy on territory held by the rebels, he added.

If it is true that UNAMID works with Sudan security agents, then we will ask the U.N. to fire the head of the UNAMID force, he said, adding JEM was holding peacekeepers from Senegal, Yemen and Ghana.

UNAMID spokeswoman Susan Manuel declined to comment, saying only: There is a situation on the ground unfolding since yesterday which we're trying to resolve.

Mainly non-Arab rebels took up arms in 2003, complaining the central government had left the region economically and politically marginalized. Khartoum mobilized troops and mostly-Arab militias to quell the unrest.

The International Criminal Court has charged Bashir with masterminding genocide and other crimes in the region, accusations Khartoum dismisses as political.

JEM is part of an alliance of Sudanese rebels groups in Darfur and southern border states which have vowed to overthrow the government of Sudanese President Omar Hassan al-Bashir.

International efforts to broker peace in the region have so far faltered, hindered by fighting and rebel divisions.

In July, Qatar brokered a peace deal between Sudan and the Liberation and Justice Movement (LJM), an umbrella group of rebel factions. JEM has refused to sign it.

While violence has died down, law and order have collapsed in some areas and attacks by criminals, militias, soldiers and tribal groups have continued.

Rebel groups such as JEM have accused the head of UNAMID, Ibrahim Gambari, of being close to the Sudanese government.

Gambari, a former Nigerian foreign minister, has dismissed the criticism and said he is willing to meet JEM and other rebels to persuade them to join the Qatar agreement.

Gambari sparked a political storm when he met Bashir during the January wedding between Chad's President Idriss Deby and a daughter of Musa Hilal, an alleged leader of Sudan's infamous Janjaweed militia

The United Nations told Gambari this month to avoid similar encounters in the future.

(Reporting by Khalid Abdelaziz and Ulf Laessing; Editing by Andrew Heavens)