We are confident that this is an agreement that will hold

SPLM/SPLA leader John Garang

"We are one and the same again," said John Garang, leader of the Sudan People's Liberation Army (SPLM/SPLA).

Mr Garang's movement is to merge with the Sudan People's Defence Force (SPDF), led by Riek Macher, which split from the SPLM in 1991 amid factional fighting.

Sudan has been wracked by civil war since 1983. Rebel groups from the Christian and animist south have not only fought the Muslim government in Khartoum, but have also frequently clashed among themselves.

Mr Garang told the BBC the two groups had agreed on "collective leadership" and would elect a leader at a convention to be held this year.

'History changes'

Mr Garang said he did not believe Mr Macher's group would again seal its own peace agreement with the government, which it did in 1997.

That deal collapsed three years later.

"You are talking about the past, of course nobody can foretell the future," he said after the deal was announced in Nairobi.

Sudan's war has led to widespread hunger

"Things do change, history does change. We are confident that this is an agreement that will hold," he added.

For his part, Mr Macher said he believed the merger would strengthen the rebels' cause on the international political and diplomatic front.

"We will make our case more strongly because we are now united," he said.

"We hope the international community will help resolve this war," he added.

In November, Mr Macher called on the United States Government to extend its war on terrorism to the Khartoum government, which he alleged was sheltering members of Osama Bin Laden's al-Qaeda network.

But Mr Garang said there had been no US pressure behind the merger of the two rebel groups.

"This agreement was achieved without external mediation and without external pressure," he said.