SAN'A, Yemen (AP) _ Northern forces bombarded the besieged southern stronghold of Aden, reportedly killing at least 36 people, as 900 foreigners who fled the city by ferry reached safe haven in Africa on Friday.

The heavy fighting came despite northern President Ali Abdullah Saleh's announced willingness to agree to a cease-fire. Five previous truces declared during the 6-week-old civil war have failed within hours.

U.N. envoy Lakhdar Brahimi, arriving in Cairo, Egypt, late Friday, said he asked both sides to send delegates to a meeting Sunday in Cairo ''to discuss the possibility of creating a ceasefire mechanism.''

He did not say whether his proposal had been accepted. But on Thursday, a diplomat close to the U.N.-mediated negotiations said Saleh and secessionist southern leaders had agreed to such a meeting at a site to be determined.

The diplomat spoke on condition of anonymity.

The 4-year-old union of North and South Yemen collapsed into civil war May 4 amid feuding between Saleh and his former vice president, Ali Salim al- Beidh, the southern leader. Northern forces hold most of the country.

Saleh refuses to meet with al-Beidh, but has agreed to hold talks with other southern leaders, said U.N. spokeswoman Therese Gastaut.

The Kuwait News Agency, which has a correspondent in Aden, said the 36 dead, most of them civilians, were among 170 casualties recorded in the shelling of Aden over the previous 36 hours. It said more deaths were expected.

The north, which appeared to be tightening its noose around Aden, warned southern civilians to stay away from strategic targets, including the south's military headquarters, radio and television buildings and offices of the south's ruling Socialist Party.

Reports from the city indicate increasing shortages of food, water and medicine, with the prewar population of 350,000 swollen by refugees.

The 900 foreign evacuees included Americans, Britons, Tunisians and Palestinians, said Jean Francois Golay of the International Committee of the Red Cross.

It was the biggest evacuation from Aden since the fighting began. Most foreigners have already left San'a, the northern capital, but Aden was spared fighting in the early days of the war.

The evacuees arrived in Djibouti, 155 miles across the Gulf of Aden on the Horn of Africa. The ferry was operated by the Geneva-based International Organization for Migration. It was not clear if further evacuations were planned.

Violent battles also resumed on the Abyan front, 25 miles east of Aden, the Kuwaiti agency reported. It said southern warplanes flew more than 20 sorties and succeeded in halting the north's advance on that front.

The agency also quoted a military source in Aden as saying southern warplanes raided the northern cities of Taiz and Hodeida in retaliation for the shelling of Aden. Northern officials did not immediately confirm the raids.

Despite the fighting, the government said it has agreed to a proposal by Brahimi to broaden a multinational military commission to supervise a new cease-fire.

The northern leadership agreed to expand the 18-member commission to include officers from Syria and Morocco, Foreign Minister Mohammed Salem Bassandwah said on San'a television Friday night.

The panel, which was set up before the war but failed to prevent hostilities, currently comprises military officers from Yemen's warring sides, Jordan, Oman and the U.S. and French military attaches in San'a.

Brahimi's proposal was designed as a compromise between southern demands for a large international force to monitor a truce and the north's rejection of further outside intervention in what it considers an internal conflict.

In Aden, the southern leadership urged the U.N. Security Council to brand Saleh and his government ''war criminals.'' Southern Aden Radio quoted the southern foreign minister, Abdullah Abdel al-Majid al-Asnaj, as saying the north had embarked on a ''dangerous military escalation'' and was ''attacking cities and residential districts.''