Congo rebel leader Laurent Nkunda stands at his base in Tebero, north of Goma in eastern Congo. (Karel Prinsloo/Associated Press)

In a startling turn against its former ally, Rwanda has arrested Congo rebel leader Laurent Nkunda after he fled a joint operation launched by the armies of the two nations, a Congolese military spokesman said Friday.

Rwandan and Congolese troops converged Thursday on Nkunda's stronghold in the Congolese town of Bunagana on the Ugandan border, said Capt. Olivier Hamuli, a spokesman for the joint force.

But Nkunda resisted arrest and fled farther south, crossing the border into Rwanda where he was taken into custody, he said.

Rwandan officials could not immediately be reached for comment and the reason for Nkunda's arrest was not immediately clear.

But analysts say Rwanda and Nkunda's own commanders had grown irritated by Nkunda, viewing him as a flippant, authoritarian megalomaniac who allegedly embezzled money from rebel coffers.

Around 4,000 Rwandan soldiers entered Congo this week at the invitation of Congo's government, a startling reversal of alliances between the two longtime enemies.

Both nations have said the Rwandans are in Congo as part of an operation to hunt down and disarm thousands of mostly Hutu ethnic fighters who fled to Congo in the wake of Rwanda's 1994 genocide.

Rebel group splits

Nkunda was the rebel leader behind months of fighting late last year with the army in eastern Congo. The fighting displaced more than 250,000 people as Nkunda's forces advanced toward the provincial capital, Goma.

Nkunda took up arms several years ago with backing from formerly close ally Rwanda, claiming he needed to protect minority Tutsis from the Hutu militias.

Earlier this month, Nkunda suffered a major blow when his ex-chief of staff, Bosco Ntaganda, formed a splinter movement. And in a dramatic reversal last week, Ntaganda announced his forces would work together with Congo's army to fight the Hutu militias and eventually integrate into the army.

Ntaganda may have turned on his former boss because he was afraid months of growing distrust might have prompted Nkunda to turn him over to the International Criminal Court in The Hague, where he is wanted for the alleged forced conscription of child soldiers in the northern Ituri region five years ago.

Though details of the agreement to allow Rwandan troops on Congo soil have not been made public, analysts speculate the government may have promised not to hand Ntaganda over for extradition in exchange for his co-operation.

Rwanda has been under international pressure for months to use its influence over Tutsi rebels to end the conflict, and the breakthrough agreement may have been borne out of the split within Nkunda's movement that both Congo and Rwanda were quick to exploit.

Nkunda has spent much of the last decade-and-a-half embroiled in war in the region. As a young Congolese in exile in Uganda, he fought with Tutsi-led Rwandan forces that stopped Rwanda's genocide 15 years ago, ousting that country's Hutu government.

He went on to become a senior commander within a Rwandan-organized Congolese rebel group, which held a huge swath of the east during a 1998-2002 war.

After a peace deal ended that fighting, he joined Congo's army but quit in 2004 to launch his rebellion. Since then, Nkunda has commanded thousands of fighters in the rural hills of eastern Congo, running his own fiefdom, collecting taxes and launching military operations against the army and Hutu militias.

In September 2005, Congo's government issued an international warrant against Nkunda for alleged war crimes and human rights abuses, though it was never able to arrest him.

The New York-based rights group Human Rights Watch says it has documented summary executions, torture and rape committed by soldiers under Nkunda's command, both in the central city of Kisangani in 2002 and in the lakeside city of Bukavu which Nkunda's forces captured briefly in 2004.

During the latest fighting in east Congo last year, Human Rights Watch says Nkunda's fighters massacred dozens of civilians in the town of Kiwanja after skirmishing with a pro-government militia group known as the Mai Mai.