Sudanese authorities have detained suspects in the killings of four Nigerian peacekeepers in Darfur, state radio said on Tuesday, after UN chief Ban Ki-moon urged swift justice in the case.

"The authorities arrested those who are involved in the attack on UNAMID (the UN-African Union Mission in Darfur) near El-Geneina, in West Darfur," Radio Omdurman reported in an SMS news alert which gave no more details.

The Sudanese Media Centre, which is close to the security apparatus, issued a similar brief report.

UN sources say the attack on October 2 was the deadliest in UNAMID'S nearly five-year history.

Ban was "appalled and deeply saddened" by the ambush, his spokesman Martin Nesirky said last week.

"The secretary general urges the government of the Sudan to conduct a full investigation and to ensure that the perpetrators are swiftly brought to justice," Nesirky said.