SARAJEVO -- Bosnian Serb forces besieging Sarajevo launched a mortar barrage toward government army positions in the city Thursday and battered the Bihac enclave, rocking a truce that has held since Jan. 1, UN officials and witnesses said.


In Sarajevo, machine-gun fire rattled soon after the explosions hit in the vicinity of the Jewish cemetery. The front line separating the mainly Moslem government army and the Bosnian Serbs runs through the cemetery.


"What we know is that at about 5.30 [p.m.] there were eight explosions in the vicinity of the Jewish cemetery from the BSA [Bosnian Serb army] side. Now everything is quiet," a UN spokeswoman, French Captain Miriam Souchaki, said.


There was no word on possible casualties, but one correspondent said the explosions reverberated through the city near the Holiday Inn hotel.


A UN spokesman described the infantry and artillery attack on Bihac as a "calculated and deliberate" assault.


"At around 10 a.m. Bosnian Serb Army 2nd Corps launched an infantry attack on the area of Vedro Polje and Klokot, which are within the Bihac 'safe area,'" the spokesman said. UN observers counted 208 shells hitting the area, with at least two falling within Bihac town itself.


Commenting on the Sarajevo attack, a UN spokesman in Zagreb said the Serbs unleashed the mortar barrage because the government troops had dug trenches in violation of the truce accord.


The Bosnian Serbs have been besieging Sarajevo for more than 1,000 days.