The return of good weather sparked a dramatic surge in combat along Bosnia's major battlefronts, U.N. peacekeepers reported Tuesday.

Heavy snows had subdued fighting last week on two fronts where the Muslim-led government army had been waging offensives.But Monday and early Tuesday combat on the northern front near the city of Tuzla escalated to its most intense level since the offensive began March 20. Military observers recorded 1,800 artillery rounds as well as heavy machine gun and small arms fire over the past 24 hours in the Majevica mountains.

There was also heavy fighting on the other main front around Mount Vlasic in central Bosnia, said U.N. spokesman Maj. Herve Gour-melon, who attributed the surge to the return of warmer spring weather.

There was no immediate indication who had the upper hand today. U.N. officials, acknowledging their information was spotty due to uncertain communications and restrictions on U.N. observers, said they had detected no signs of major battlefront gains or losses in either region.

Last week, government soldiers made the most gains.

The exception to the escalation was the Bihac pocket in northwest Bosnia, where decreased shelling was reported Tuesday. A U.N.-protected safe zone in the enclave had been shelled by the Serbs for four straight days through Monday, provoking U.N. protests.

Kris Janowski, a UNHCR spokesman, said Bosnian Serbs denied passage to two convoys planned for two eastern Bosnian enclaves, Gorazde and Srebrenica.

But a convoy laden with food for nearly 200,000 hungry people struck out for the Bihac pocket today, trying to reach it through Petrovo Selo, a Croatian town on the border with Bosnia held by rebel Croatian Serbs.