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ADDIS ABABA, Ethiopia (CNN) -- Amid renewed fighting in Congo, African and U.N. leaders tried Thursday to achieve peace in the former Zaire despite three previous failures.

Rebels trying to oust President said they had seized the towns of Shabunda, 250 kilometers (150 miles) southwest of their stronghold at Goma, and Aru, 100 km (60 miles) south of the Sudanese border. In other unconfirmed reports:

• Rebel-run Radio Bukavu also said insurgents and government-backed militiamen clashed near Bukavu, a lakeside town on the border with Rwanda.

• Refugees fleeing across Lake Tanganyika to Tanzania told U.N. workers that the government recaptured the southeastern town of Kalemie on Wednesday.

The rebels trying to unseat Kabila claim he has failed to implement democratic reforms and has worsened ethnic hatred.

Kabila said Thursday that his year-old government is preparing for a "long-haul war" against the rebels and will launch further offensives in the east of the country.

His statement, carried on state radio in the Congolese capital of Kinshasa, came as leaders from neighboring countries embroiled in the war met for a two-day peace conference. The aim of the gathering in the Ethiopian capital of Addis Ababa was to work out a cease-fire and withdrawal of outside troops.

Rebels were not invited, said Ibrahim Dagash, spokesman for the Organization of African Unity, host of the latest round of talks.

A Congolese rebel delegation stormed out of negotiations in Zimbabwe on Tuesday, just before a draft of a cease-fire agreement was expected to be signed. Fighting immediately surged in eastern Congo.

Among those attending the peace conference were government ministers from Zimbabwe, Angola and Namibia, whose armies have backed Kabila. Congo sent its foreign minister.

Representatives from Uganda and Rwanda, which Kabila claims are supporting the rebels, also were taking part in the talks.

Rwanda denies its troops are backing the rebels. Uganda admits it has troops in Congo, but says they are only protecting its borders from attack by Ugandan rebels.

Zambia, which has remained neutral, sent its defense minister.

OAU Secretary-General Salim Ahmed Salim and a team of U.N. advisers also were attending.

The failed summit in Victoria Falls, Zimbabwe, marked the third formal attempt at a peace deal since the conflict began August 2, and the only time rebels were invited.

Kabila's government asked Zimbabwe to arrest eight Congolese rebels who flew to Victoria Falls for the talks, the Financial Gazette reported Thursday.

Justice Minister Emmerson Mnangagwa said Zimbabwe had no jurisdiction to do so.

The Associated Press and Reuters contributed to this report.