Two Jordanian peacekeepers have been freed after 136 days of captivity in Sudan's Darfur region, the African Union-UN mission to the troubled region said on Wednesday.

"They are safe," UNAMID spokeswoman Aicha Elbasri told AFP. "This is the longest hostage-taking incident (for UNAMID)."

She said the peacekeepers were now on their way to Khartoum and then Jordan after their release in Zalingei, capital of the recently-created Central Darfur state.

They went missing on August 20 in Kebkabiya town, about 140 kilometres (87 miles) west of El Fasher, the capital of North Darfur state where the UN has warned in recent months of rising insecurity.

Their release was welcomed by Jordan's police directorate.

"Police corporals Hassan Mazawdeh and Qasem Sarhan are now at the Jordanian mission, enjoying good health," the kingdom's Public Security Directorate said in a statement, without elaborating.

"We thank the Sudanese government and the United Nations for their help, support and coordination," it added.

"We are currently in contact with the Sudanese government and the United Nations to ensure the safe return of the two corporals as soon as possible."

Jordan's police directorate said at the time that the pair disappeared while they shopped in the Kebkabiya area.

They were among a group of peacekeepers buying supplies in a market but they failed to show up at a pre-arranged meeting point at the end of the trip, the police said.

There has been no indication as to who may have abducted them.

Recent years have seen a wave of kidnappings for ransom in Darfur, where ethnic rebels a decade ago began an uprising against the Arab-dominated Khartoum government.

Although violence is down from its peak, villages have been razed and rebel-government fighting, banditry, inter-Arab and tribal disputes continue to afflict the region, in Sudan's far west.

Last May, unknown captors released a British employee of the UN's World Food Programme who had been held for nearly three months in Darfur.

In February, rebels of the Justice and Equality Movement freed five Turks they held captive for several months.

That followed the release in December 2011 of Italian hostage Francesco Azzara, a humanitarian worker abducted for about four months. UNAMID blamed a "criminal element".

That same year three Bulgarian helicopter pilots working under a UN contract were held for 145 days.

An analyst has told AFP that it is often known very quickly who the kidnappers are, but negotiations take time.

Chances that the suspects will be brought to justice are slim because "there are too many links between the government people, (and) the tribes", said the analyst who declined to be named.

It was not immediately clear how many UNAMID members have been taken hostage during the five-year history of the world's largest peacekeeping mission.

Forty-three UNAMID peacekeepers have been killed in hostile action, including five in October.

Dane Smith, the US administration's senior adviser for Darfur, said in December that both militia and bandits have attacked UNAMID peacekeepers and although the Sudanese government has announced investigations "there never are any results".