Serb gunners concentrated their fire along the northern front lines of Sarajevo Thursday, and Serb forces reportedly were attacking troops of the Muslim-led government in northern Bosnia.
Shelling of Sarajevo had eased for several days before Wednesday, when 350 rounds hit the area, said a U.N. spokesman, Maj. Idesbald van Biesebroeck.State-run Bosnian radio reported heavy Serb shelling of the besieged Muslim enclaves of Maglaj and Tesanj in the north, where there were reports last week that Muslim-led government forces had broken through siege lines.
There have been signs of intensified efforts by Bosnian Serbs to reverse recent military gains by the government, the biggest overall loser so far in the war set off by Bosnia's secession from Serb-dominated Yugoslavia.
In Belgrade, the Yugoslav capital, a U.N. official said that Bosnian Serb refugees in Yugoslavia are being ordered to report for service with the Bosnian Serb army, a possible sign of preparations for more heavy fighting.
Units of the regular Yugoslav army's special forces brigade have been reported helping Bosnian Serb forces in offensives against the strategic town of Olovo to the north of Sarajevo.
They were sent to the region after attacks by Bosnian Serbs in December failed to dislodge the lightly armed government defenders around Olovo, said a Bosnian Serb official, who spoke on condition of anonymity.
Yugoslavia, now made up only of Serbia and Montenegro, pulled its army out of Bosnia in 1992.