NAIROBI, KENYA, JAN. 5 -- More than 400 foreign nationals including Americans trapped by week-long fighting in Mogadishu, the rebel-besieged Somali capital, were evacuated today in separate operations conducted by Italian and U.S. military aircraft during a temporary break in the civil conflict.

Two U.S. naval helicopters, which arrived at the U.S. Embassy in the war-torn capital late Friday with a small contingent of Marines aboard, ferried more than 260 American citizens and other foreign nationals -- including the Soviet ambassador to Somalia -- today from the embassy compound overlooking the Indian Ocean to U.S. naval ships positioned off the Somali coast.

At about the same time, two Italian cargo planes bearing temporary Red Cross markings arrived at Mogadishu airport to begin the evacuation of 190 Italians and 70 French, German, Soviet and Ethiopian citizens. By tonight, about 200 of them had been flown to the Kenyan port city of Mombasa, 600 miles southwest of Mogadishu.

In Rome, the Italian Foreign Ministry said it was forced to halt its evacuation operation late tonight when clashes resumed in the capital despite pledges by the rebels of the United Somali Congress to cease fire until all foreigners had left, the Associated Press reported.

The evacuees got to the Mogadishu airport earlier in the day by negotiating a temporary cease-fire corridor that led from the Italian Embassy through the city, which has been the scene of horrible street fighting during the past week and is reported littered with bodies.

The route was agreed to after intense negotiations this week between the warring sides and the government of Italy, the former colonial ruler of most of what is now Somalia and the nation's closest benefactor.

The fighting between rebels and forces loyal to President Mohamed Siad Barre has cost the lives of at least 1,500 persons so far, according to the United Somali Congress, which is leading the insurgency in the East African country of 8 million people.

The rebels today rejected Siad Barre's plea for a truce offered Friday from his bunker at a military airport south of the city. They said there could be no peace until Siad Barre, accused of numerous human rights violations, left the country.

In London, a Somali rebel spokesman said Siad Barre, who has ruled Somalia for 21 years, had fled Somalia by plane to Nairobi this afternoon. But the Kenyan government denied that he was in Kenya.

The Italian and U.S. evacuations were carried out without violent incidents or injuries after the rebels had agreed to a temporary cease-fire to allow foreigners to leave the country.

The rebels had said they would allow the evacuations to proceed as long as foreign military planes were not used in the operation. In a statement Thursday, the rebels said the use of foreign military planes "could be interpreted as an intervention" on Siad Barre's behalf.

In keeping with that request, the Italian aircraft used today bore Red Cross emblems and Italian military personnel wore Red Cross insignia.

More than 500 foreign nationals, including 87 Americans, were trapped in Mogadishu when the fighting erupted. The Somali government has appealed to the world for emergency supplies of food and medicine and warned about the danger of disease outbreaks caused by bodies in the city streets.

In a statement released tonight, the U.S. State Department said the mission of the Marines in the evacuation was "solely to assist in the rapid and peaceful departure of Americans from Somalia. They are not involved in any way in the conflict there."

U.S. officials declined tonight to say where the evacuated Americans would be taken, although Mombasa seemed the most likely destination.

Meanwhile tonight, France announced plans to begin evacuation of an unknown number of French nationals sheltered at the French ambassador's seaside residence. A French frigate sent to Somalia earlier this week will presumably take part in that operation.

Two amphibious U.S. naval vessels, the USS Guam and the USS Trenton, took part in today's evacuation operation. Both ships, based in Norfolk, are in the region as part of the Persian Gulf armada deployed in Operation Desert Shield.

Staff writer Howard Kurtz in Washington contributed to this report.