WINDHOEK, Namibia (CNN) -- Congolese President Laurent Kabila said Friday he hopes his country's civil war will end by Christmas, even as rebel troops turned back an assault by Zimbabwean troops supporting his government.

Kabila made his comments during a surprise visit with Namibian President Sam Nujoma, a key ally in Kabila's four-month struggle against rebels backed by Uganda and Rwanda.

The visit came as rebel troops in Kabila's Democratic Republic of Congo turned back an assault by Zimbabwean forces allied with the Congolese government. At the same time, preparations for new cease-fire talks continued.

Kabila said he was ready for the upcoming peace talks, to be held on December 14. But he warned his conditions for a cease-fire would include the withdrawal of Rwandan and Ugandan troops from Congolese territory.

"If they want to remain in the Congo, there won't be peace," he said.

Peace talks began in Paris last weekend with promises to end the fighting by mid-December. They will continue in the Zambian capital of Lusaka.

Kabila's war against the Tutsi-led insurrection has gone on for four months. In addition to Zimbabwe and Namibia, Chad and Angola are aiding his 18-month-old government.

The fighting continued near the town of Kabalo this week as rebel forces fought off an assault by Zimbabwean troops backed by tanks and aircraft.

The Zimbabwean troops attacked Thursday night and fought into Friday along the Lualaba river, the front line of the fighting.

Rebel soldiers displayed captured Zimbabwean weapons for journalists after the battle. Rebel commanders said the Zimbabwean troops suffered heavy losses.

Kabalo fell to the rebels in October. They claim they have repulsed frequent attempts by Zimbabwean troops to regain control of the city, about 750 miles (1,200 km) southeast of Kinshasa.

The rebels now hold nearly half the country, including its entire eastern region.

Also on Friday, a military court in Kinshasa, the Congolese capital, convicted a provincial governor of treason charges.

Gov. Fuko Unzola of the western province of Bas-Congo was sentenced to 15 years in jail, defense lawyers said.

The case against him was based primarily on his presence at a support rally for the rebels and his trip to the eastern city of Goma -- rebel headquarters -- several days later.

There is no appeal on the charges, but he can request a pardon from Kabila. A senior aide to the governor was also convicted of collaborating with the rebels and sentenced to 10 years in prison.

Reuters contributed to this report.