MONROVIA, Liberia ? Rebels captured Liberia’s refugee-choked second-largest city Monday, defeating President Charles Taylor’s embattled forces on a new front and depriving him of his last significant port outside the besieged capital.

The capture of the strategic city of Buchanan, 60 miles southeast of Monrovia, the capital, came as deliberations on a peace mission for the West African nation showed no sign of progress.

Gen. Benjamin Yeaten, a leading government commander, confirmed that Buchanan fell to fighters from Liberia’s second rebel group, the Movement for Democracy in Liberia, by nightfall.

Yeaten said government troops remained on the outskirts of the city and were planning a counterattack.

Taylor’s forces took off running as rebels advanced into Buchanan, said John Mensah, a resident reached by telephone there, who added the rebels were “now in complete control of Buchanan.”

During the rebel takeover, the Buchanan office of the international humanitarian group Merlin was looted, according to Merlin office workers in the capital.

The attack and quick victory at Buchanan came as Liberia’s leading rebel movement, Liberians United for Reconciliation and Democracy, pressed its bloody 9-day-old siege of Monrovia, in fighting that has killed hundreds.

“Taylor must go,” said Joe Wylie, spokesman for the leading rebel movement, saying only international “whining about civilian casualties” was stopping insurgents from a final push to topple the Liberian leader.

“He’s getting weaker and weaker,” Wylie said. “He should not face us in a final military showdown that will just take lives.”

Rebel forces now hold more than 60 percent of Liberia, grinding down Taylor’s forces in their three-year battle to oust him.

A government militia member sits in front of the scene of a mortar attack on Broad Street in the Liberian capital of Monrovia. Rebels captured Buchanan, about 60 miles away, Monday.

The Movement for Democracy in Liberia, which until recently had largely heeded cease-fire pledges, claimed Taylor’s forces had provoked the offensive on Buchanan with attacks on rebel positions outside the city in recent days.

Rebel official Boi Bleaju Boi pledged insurgents would open the southeastern city’s port up to peace forces, should they choose to land there.

Tens of thousands of refugees from the capital in recent days had flooded east into Buchanan, desperate to escape the shelling, grenade blasts and machine-gun fire of Monrovia.

On Monday, many took flight again, picking their way back along the coast toward Monrovia.

Liberian Defense Minister Daniel Chea had rushed overnight to the developing eastern front, which brings the smaller, but better-armed and better-disciplined second rebel movement into active battle against Taylor’s already stretched-thin forces.