TUTSI REBEL SHELL ZAIRE CITY (Reuters)

BUKAVU, ZaireShelling rocked the eastern Zairian city of Uvira as Tutsi rebels battled Zairian troops Friday, and a European envoy warned that a new catastrophe in,.Central Africa could be near.

Western aid workers in Geneva said that the Banyamulenge rebels had seized Uvira airport and cut off all satellite and radio communications, and that many people were fleeing the city which is on Lake Tanganyika.

Residents of Bujumbura, the capital of Burundi 30 kilometers (18 miles) to the east, said they heard blasts from Uvira overnight and on Friday from fighting between troops and the rebels.

A local UN radio operator in Uvira was quoted as saying Thursday night that he had to stop transmitting because rebels were about to take over the are.

Aid officials fear that the rebellion eastern Zaire, which burst into heavy fighting a week ago, could spread further and that Tutsi-dominated armies in Burundi and Rwanda could join the conflict. Both countries deny they are involved.

The Zairian president, Marshal Mobuto Sese Seko, is in Switzerland for chemotherapy treatment. His absence: has fueled fears the revolt might herald the breakup of Zaire.

The Banyamulenge, Tutsi who migrated about 200 years ago to what is now Zaire, say they are fighting for control of the administrative area of Kivu, the return of their property and Zairian citizenship, which had been denied to them in 1981.In Brussels, the EU humanitarian aid commissioner, Emma Bonino, appealed to the warring parties to stop fighting and avoid further genocide. She added that efforts to feed the 1.1 million refugees in eastern Zaire faced severe problems because fighting was blocking aid.

The UN High Commissioner for Refugees, Sadako Ogata, said in a message to nearly 300,000 refugees who fled last week, "I am deeply saddened that once again you are on the roads fleeing for your lives."