SARAJEVO -- An accord to end sniping in Sarajevo took effect Monday and UN peacekeeping officials hoped it would help defuse tensions between warring factions in the Bosnian capital.


The anti-sniping agreement signed Sunday went into effect at 1100 GMT and followed a marked increase in sniper fire that had claimed a growing number of civilian lives and forced the virtual closure of the city's tram system.


The Bosnian Serbs and the Moslem-led Bosnian government army also agreed verbally to end shooting attacks around Sarajevo airport which have shut down the UN humanitarian airlift to the city.


As part of the anti-sniping accord, Serb and Moslem officials pledged to form joint patrols with the UN Protection Force to flush out snipers disobeying orders and prosecute them as criminals.


Gunfire halted the airlift Thursday only two days after it resumed following an 18-day break caused by a spate of shooting incidents. The city already faces a food shortage that the United Nations says could become critical without regular deliveries.


A spokesman for the UN High Commissioner for Refugees said the relief airlift may resume on Tuesday if UNPROFOR military flights were able to land without coming under fire.


"We hope this operation will resume tomorrow. There are meetings of the countries involved today. It's likely that with the continued safe operation of the UNPROFOR flights, UNHCR humanitarian operations will also resume," he said.


Bosnian Serbs had stepped up sniping in the capital in the past month amid international pressure to accept the latest peace plan, which they have refused to endorse.


The United Nations reported on Monday mainly sporadic clashes on Bosnia battlefronts and said Bosnian Serbs had obstructed UN aid convoys in eastern Bosnia.


A UNHCR aid convoy headed to Gorazde had to turn back Sunday after Bosnian Serb forces insisted that two of nine trucks unload at the Serb-held town of Visegrad instead, Kessler said.


"This is of course totally against the clearance we had received from the Pale (Bosnian Serb) authorities. Visegrad is already served and are getting what their beneficiary figures say they require. So this kind of demand is unacceptable and disheartening," he said.


UN officers said a stalled peace plan and growing pressure to lift the arms embargo against Moslem-led forces meant that many countries were in the process of considering a withdrawal of their United Nations peacekeepers in Bosnia.