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.
Rebels from the Justice and Equality Movement (JEM) said they detained the peacekeepers, most of them from Senegal, on Sunday night in Shagied Karo in north-western Darfur, Reuters reports.
JEM earlier said there were 52 peacekeepers and accused members of the international force of travelling to the area to help Sudanese security to spy on rebel-held territory.
"All peacekeepers are free but we are holding three Sudanese accompanying them," Gibreel Adam Bilal, a spokesman for the rebel Justice and Equality Movement (JEM), later told Reuters, without going into further detail. He accused the three of working for security.
UNAMID spokeswoman Susan Manuel said the peacekeepers had been allowed to go, but were staying in the area to try and help the three civilian staff.
She denied the three were working for Sudanese security. "They are UNAMID staff," she said.
Mainly non-Arab rebels took up arms in 2003, complaining the central government had left the region economically and politically marginalised. Khartoum mobilised troops and mostly-Arab militias to quell the unrest.
The International Criminal Court has charged Sudanese President Omar Hassan al-Bashir with masterminding genocide and other crimes in the region, accusations Khartoum dismisses.
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.
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