SARAJEVO -- The top Bosnian Serb general on Monday rejected a NATO ultimatum to withdraw heavy weapons from around Sarajevo. His defiance set the stage for renewed airstrikes within hours.


"No one, not even myself, has the right to order the withdrawal," said the letter, received less than three hours before an 11 p.m. deadline for new NATO attacks. "This is a political question which is not in the jurisdiction of generals."


The letter, addressed to Lieutenant General Bernard Janvier, the UN commander in former Yugoslavia, appeared to negate one received earlier at regional UN headquarters in Zagreb, Croatia, and signed by Nikola Koljevic, chief deputy of Bosnian Serb leader Radovan Karadzic.


Koljevic signaled "overall compliance" with UN demands, including pulling back the heavy weapons menacing the Bosnian capital, said UN officials.


But with Mladic, who has defied his political peers before, refusing to bow to the UN ultimatum, the prospects of renewed massive airstrikes grew.


Mladic suggested Koljevic and Karadzic also had no right to decide on a pullback, saying that could only be ordered by the self-styled parliament of the rebels after a popular referendum also opted for such a withdrawal. That is something neither NATO or the United Nations, which have been pressuring the Serbs for a quick response to their demands, are likely to agree to.


The differing signals highlighted the differences between Karadzic and Mladic, whose rivalries exploded recently after Karadzic tried to fire his general. Mladic ignored the Bosnian Serb leader, who then was forced to rescind his dismissal.


Clearly feeling the pressure of the looming NATO airstrikes, Mladic, in his letter, offered a unilateral cease-fire by his forces besieging Sarajevo if the air attacks were called off.


The letter, a copy of which was faxed to the Belgrade buro of The Associated Press, called for an urgent meeting of military commanders of the warring sides that would result in "complete, permanent and unconditional cessation of hostilities" in Bosnia.


"Until that meeting is convened, I unilaterally proclaim cessation of hostilities in the region of Sarajevo, where we will not undertake any actions except in cases of self-defense," the letter said.


Mladic's offer of a unilateral cease-fire appeared to be a repeat of a statement earlier in the day where he said he was willing to halt attacks on Sarajevo or the other safe areas.


He also said he would withdraw heavy weapons under conditions negotiated by military commanders of the opposing armies. He called for a cease-fire across Bosnia, and demanded that NATO stop flying over Serb-held territory.


Mladic in addition promised to ensure free access for the United Nations and humanitarian organizations around Sarajevo.


But those offers were dismissed by UN officials as too little or irrelevant to what was being demanded.


The Serbs were anyway allowing traffic to cross over the Sarajevo airport and into the city from government-held territory on the south side Monday.