SARAJEVO, Bosnia-Herzegovina (AP) _ Serb troops unleashed their artillery on Sarajevo before dawn today, raining hundreds of shells on the besieged Bosnian capital in an attack that again blocked vital U.N. aid flights.

Fighting also flared in other parts of Bosnia, further dimming prospects for planned peace talks among leaders of the country's three warring ethnic factions Jan. 18 in Geneva.

The thud of explosions began spreading across Sarajevo at 6 a.m., a day after the city shuddered through one of the worst bombardments in months.

''Sometimes artillery firing couldn't be counted because of the intensity of the shelling,'' said Maj. Idesbald van Biesebroeck, spokesman for U.N. peacekeepers in Sarajevo.

At least two people were killed and 32 wounded Wednesday, but the toll was expected to go higher. At least 31 people have died and dozens have been wounded in Sarajevo since New Year's Day.

The airport west of the city also came under fire, forcing its closure Wednesday and today. Aid flights provide Sarajevo's 380,000 citizens with almost all their food and medicine.

Despite the shelling today, friends and relatives gathered to bury six family members who were killed by a single shell blast as they sat down for a meal Tuesday.

''Does anybody in the world care or have nightmares because of what happened to us?'' cried Maja Dragnic, 16, one of the few surviving relatives.

Van Biesebroeck reported that artillery shells also hit the center of Zenica, a predominantly Muslim town in central Bosnia used by the United Nations as a staging point for aid distribution.

Fighting between Croat militiamen and troops of Bosnia's Muslim-led government escalated in central and southwestern Bosnia following the failure of peace talks between the two groups Wednesday in Vienna, Austria.

Croat and government forces initially fought together against Bosnian Serbs, who grabbed control of 70 percent of Bosnian territory after the Muslim-Croat majority moved in April 1992 to secede from Serb-dominated Yugoslavia. But the alliance has since collapsed.

More than 200,000 people are believed to have been killed in 20 months of war.

Van Biesebroeck complained of serious aid distribution problems around Kakanj, 25 miles northwest of Sarajevo, saying that some local officials were delivering food to government troops before civilians.

But he added: ''I don't want to blame any (side) more than the other'' for interfering with aid efforts. ''They are all guilty.''

U.N. officials estimate that as many as 3 million Bosnians, most of the people still in the country, need outside aid to survive another winter of war.