At least five people were killed and 26 wounded in the city. Civilian casualties were limited as most people took cover when the general alert sounded before 8am. The bombardment began about one hour later and lasted most of the day, until a UN-brokered lull at around 4pm. "We've got verbal agreements from both sides not to fire except in self-defence," said Alex Ivanko, a UN spokesman in Sarajevo.
Much confusion surrounded the fighting, whioch was probably the worst since Nato imposed a heavy-weapons exclusion zone around the city in February 1994. The spark apparently came from four Bosnian mortar bombs fired at a Serb barracks. But the UN said both sides were "equally to blame". The fighting revolved around land from which the Bosnian army can attack the road to Pale, the Serbian "capital".
"Once again it is the civilians who become the ultimate victims of this tragic war," Mr Ivanko said. "They should not be put through another harrowing day of seeing shrapnel and bullets tear people apart." Azra Buljubasic, 12, was one of the first casualties, killed by shrapnel that seriously injured her 17-year-old brother Nedim. He is not expected to survive.
Ratko Mladic, the Bosnian Serb commander who has ignored the UN for two months, talked to the peace-keepers yesterday and promised to refrain from attacks on civilians and the UN. His forces appear to have exercised restraint.
Dust, shattered glass and chunks of fallen masonry distinguished new craters from old, the result of Serb shells. From the city it was possible to hear the course of some government fire: the hollow boom of outgoing mortar bombs, the whistling journey across the valley, the dull thump of an impact on the green hills above.
The road to Pale, the small ski-resort that houses the Bosnian Serb leadership, is visible from the city, running above a Serb trench line and past a few ruined buildings, some of which were burning yesterday. It had long been safe from government attack, but in the past few days the Bosnian army has moved into no man's land, a swathe of steep, rocky land on a hill called Debelo Brdo, and into range.
The UN said the government army was the first to fire proscribed heavy weapons: four mortar bombs at a Serb barracks close to the city. But at lunchtime Bosnian Serb soldiers launched an infantry attack into no man's land on Debelo Brdo. UN officials are unsure whether this came in response to the mortar fire, to the targeting of the Pale road, or had been planned in advance.
It does not seem that the fighting was a Bosnian attempt to break the siege of Sarajevo, which has slowly but inexorably tightened as the Bosnian Serbs turned the screws. The city's gas supply has been cut in half by the Serbs, effectively stopping domestic supplies; the only land route in has been shelled and shot at repeatedly; and the UN aid airlift has been down for almost six weeks.
The UN mans an observation post close to Debelo Brdo. The peace-keepers might have a better idea of the fighting when their comrades feel it is safe enough to do more than shelter in their bunker.
Nato, which is entitled to bomb heavy weapons inside a 20km zone around Sarajevo, sent jets roaring over the city as requested by the UN, which rejected government demands for air strikes against the Serbs.
"Both sides have been firing heavy weapons within and without the total exclusion zone," Colonel Coward said. "We're not in a position to apportion blame in this instance."