KAMPALA, Uganda—The biggest rebel group in the Democratic Republic of the Congo on Tuesday declared an end to its 20-month insurgency, after government troops earlier in the day drove fighters from their last remaining strongholds near the Ugandan border.

People displaced from fighting in the Democratic Republic of the Congo troops gather in the eastern city of Rutshuru.

The end of the so-called M23 rebellion sets up the prospect of peace in one of the world's most mineral-rich countries. But while the rebellion that hurt the country's mining industry has fizzled out, the fighting hasn't entirely stopped. Various armed groups continue to roam Congo's eastern region and scattered clashes continued on Tuesday.

The leader of the rebel group known as M23, Bertrand Bisimwa, said his commanders had been asked to prepare to disarm and demobilize their fighters. In a statement released earlier Tuesday from Uganda, where Mr. Bisimwa has taken refuge, the M23 leader said he decided "to put an end to its rebellion and to pursue with purely political means the search for solutions to the deep causes that led to its creation."

Peace talks have started and stopped repeatedly over the past year. Now, the defeat and scattering of the remaining M23 rebels means the government can reject previous demands of amnesty for their military commanders and pursue war-crimes charges against some of them.

Lambert Mende, the DRC's information minister, said Congolese troops, backed by United Nations helicopters and tanks, had earlier dislodged around 200 fighters from hills bordering Uganda. The Congolese army has driven M23 rebel fighters from their bases in gold- and tin-mining towns following a rapid offensive over the past two weeks.

"Most rebels are surrendering, others have crossed into Uganda and Rwanda," he said. "It is a great victory for our gallant soldiers."

The U.N.'s role in the rebels' defeat has proved pivotal. In August, a U.N. combat brigade began enforcing a security zone around the strategic city of Goma and assisting a government offensive. A string of government victories followed….

A statement from U.N. Secretary-General Ban Ki-moon and representatives from the African Union, European Union and U.S. welcomed an end to the rebellion, and it urged M23 and the Congolese government to sign a "principled agreement that ensures the timely disarmament and demobilization of the M23 and accountability for perpetrators of war crimes and crimes against humanity."

Analysts who have followed the violent twists and turns of two decades of fighting in the country cautioned that peace would be elusive so long as such groups remained active. The army's victory, said Jason Stearns, a Congolese expert with the Nairobi-based Rift Valley Institute, is "a step in the right direction, but more concerted efforts are required to consolidate peace.”…