Also in this story:

• Angolan troops take air base
• Air power could be decisive
• Rebels claim Kisangani
• Related stories and sites

KINSHASA, Congo(CNN) -- While both government troops and rebels in the Democratic Republic of Congo claimed territorial gains Sunday, Southern Africa leaders attending an emergency summit called for a cease-fire in a conflict that has already drawn in neighboring nations.

"There should be a cease-fire. There should be a standstill followed by a process of political negotiation," South African President Nelson Mandela said after a meeting of the Southern African Development Community in Pretoria, South Africa.

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The rebels advance towards Kinshasa

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SADC members

The members of the Southern African Development Community are Angola, Botswana, Lesotho, Mauritius, Malawi, Mozambique, Namibia, Seychelles, South Africa, Swaziland, Tanzania, Zambia, Zimbabwe and the Democratic Republic of Congo -- formerly Zaire.

"The summit committed itself to seek an end to the conflict," the leaders said in a communiqué issued by the 14-nation SADC.

The call for a cease-fire came the same day that rebels lost a key air base near Congo's Atlantic coast but claimed to have taken control of another key commercial city in the northeast.

Angolan forces supporting President Laurent Kabila of the Democratic Republic of Congo captured the air base in the town of Kitona.

"The Angolans are at the base and have captured a large cache of weapons and ammunitions," said a government official in close contact with Kabila.

A rebel commander confirmed that the base had fallen to the Angolans, who reportedly used tanks in the battle in a drive out of Angola's Cabinda province.

Observers say the Angolans may now use the base as a staging ground for attacks against the rebels, who claim to be only 30 km (19 miles) from the capital, Kinshasa.

Angola has the best equipped air force on the continent after South Africa, and analysts have said that its intervention in the widening Congo conflict could be decisive.

On Saturday, Reuters news agency correspondents with the rebels witnessed two MiG-21s firing on rebel positions. The rebels said they suspected the planes were Angolan or Zimbabwean, as Kabila does not have any MiGs.

Angola has been tight-lipped over the weekend about rebel allegations of its involvement, though it has declared its willingness to back Kabila.

In return, regional analysts say, Angola hopes to use its influence to pressure Kabila to choke off key supply routes to the UNITA rebel movement in Angola.

Congo's Interior Minister Didier Mumegi would only say that the Angolans "are deploying beside our Congolese forces to reinforce and protect our army."

Zimbabwe also has sent troops and equipment to aid Kabila's government. Some reports say 600 Zimbabwean troops are west of Kinshasa, leaving rebel forces between the Angolan and Zimbabwean allies of Kabila.

While suffering a setback in the west, the rebels claimed a major territorial success in the northeast, saying they had captured the city of Kisangani on Sunday.

"Our troops have arrived in Kisangani and Kisangani has fallen under our control," rebel leader Earnest Wamba dia Wamba told a news conference in the eastern town of Goma.

Kisangani is the last navigable port on the Congo River, and the main commercial center for the northeast of the vast country.

When Kabila took Kisangani from Zairian President Mobutu Sese Seko's forces in March 1997, it proved a turning point in the war that brought him to power two months later.