The two sides have agreed the truce in an effort to bring peace to Sudan's western Darfur region, where a sporadic conflict has raged since February.

Under the agreement, both the government and the rebels promised to free prisoners of war and address issues of underdevelopment in the region.

The announcement comes on the third day of separate talks between the government and the main rebel Sudan People's Liberation Army (SPLA) aimed at ending the country's 20-year civil war.

"The government kept its pledge and freed today all 54 detainees from different government prisons," said Presidential Affairs Minister Al-Tayeb Ibrahim Mohammed Khair.

He said it "signals the start of the ceasefire" signed with the SLM in Chad on Wednesday.

Mr Khair said Khartoum expected the SLM to reciprocate by freeing its prisoners, although he acknowledged it was not known how many were being held.

Big gulf

The Darfur rebels have accused Khartoum of arming Arab tribes to stage attacks on non-Arab communities and have fought for an end to marginalisation in the region.

The Sudanese army declared its commitment to the ceasefire, with spokesman General Mohammed Beshir Suleiman saying the forces "would support and safeguard" its implementation.

The talks are seen as crucial to ending Sudan's civil war

Meanwhile, the first face-to-face talks between SPLA leader John Garang and the Sudanese Vice President Ali Osman Taha continue into a third day in Kenya.

The talks are seen as critical to ending a long-running civil war between the mainly Christian rebels in the south and the Islamic government of the north that has cost some two milion lives.

Negotiations stalled last month when the government refused to approve the final draft of a deal to share power with the rebels.

A ceasefire has more or less been holding on the ground in southern Sudan, but the rebels have made it clear that a big gulf remains between the two sides.

"The issues of the presidency, the issues of wealth sharing, the issue of security arrangements, the issues of power sharing, and the issue of the three conflict areas are the major issues that are outstanding," said Mr Garang earlier in the week.