Kinshasa, Congo ? In a stunning reversal of alliances, Rwandan troops captured Congo’s most powerful rebel leader, a longtime ally who the Congolese government says was at the heart of years of war in the east, officials said Friday.

Congo applauded the surprise arrest, hoping it would herald a new era of peace and mark the end of the Central African nation’s Tutsi rebellion. But few believe the country’s problems are over and many fear the unprecedented and unpopular deal with former enemy Rwanda is a risky gamble that could unleash more bloodshed.

Rwanda detained Laurent Nkunda apparently as part of an agreement with Congo that opened the way for thousands of Rwandan soldiers to cross the border this week in a joint operation to hunt down Rwandan Hutu militiamen.

The region has been mired in conflict since Rwanda’s 1994 genocide spilled war across the border and Hutu militias sought refuge here. Rwanda has invaded twice to eradicate the militias — though it was accused of plundering Congo’s great mineral riches instead. The militia’s presence also gave birth in 2004 to Nkunda’s rebellion, whose raison d’être was defending minority Tutsis against Rwandan Hutus.

It was a remarkable fall from grace for Nkunda, who only weeks ago had forced Congo’s embattled government to negotiate at peace talks in Kenya after his fighters advanced to the outskirts of the regional capital, Goma, forcing more than 250,000 people from their homes.