Bosnian Serb leader Radovan Karadzic agreed on Tuesday to open the airport at the besieged Bosnian town of Tuzla for humanitarian flights, in a potential breakthrough deal reached with Russian Foreign Minister Andrei Kozyrev.


The deal, reached during a visit by Karadzic to Moscow, is contingent on the stationing of Russian observers in Tuzla to ensure that the airport would not be used for military purposes.


"The blockade of the airport of Tuzla will be lifted with the participation of Russian observers and strictest control to ensure that only peaceful, humanitarian cargos are delivered to the region," Kozyrev said after a two-hour meeting with Karadzic.


Following hard on the heels of Russia's diplomatic coup in persuading Serb forces to withdraw from the Bosnian capital of Sarajevo two weeks ago, the agreement drew cold initial responses from Bosnian Moslem and United Nations officials.


Kozyrev said the agreement had been negotiated on instructions from President Boris Yeltsin and represented a large step towards a political solution of the crisis.


"We will be asking president Yeltsin to take a decision that one of the first planes to land in Tuzla should be Russian," Kozyrev added.


Karadzic said the Bosnian Serbs had never been against opening the airport for humanitarian deliveries, but that "now we believe that Russian observers will ensure that it is not used for military purposes." The deal drew a swift and critical reaction from Bosnia's vice president, Ejup Ganic, who called it "an insult to the United Nations," according to Reuters.


"We were not consulted," he said. "This technique of injecting Russians into the situation is unacceptable."


Ganic referred to the Sarajevo deal, under which Bosnian Serb forces agreed to withdraw heavy artillery from around the city only when Russia promised to send 400 troops to the Bosnian capital.


A UN official, Colonel Simon Shadbolt, was quoted as saying that airport opening was "another example of Russians jumping on the success wagon."


He also wondered if Russia would be allowed to implement the accord.


"The Russians' job will be the decision of the sector commander," Shadbolt said. "Countries sometimes specify where they want their troops to serve but we won't allow them to tell us what job their troops will be performing. That won't happen."


Karadzic arrived in Moscow on Monday, when he had a meeting with Vitaly Churkin, Yeltsin's special envoy to the former Yugoslavia, said a Churkin aide.


Before seeing Kozyrev, Karadzic visited Metropolitan Kirill, who heads the foreign relations sector of Russia's Orthodox Church, which backs the Serbs.


Kozyrev and Karadzic reached the agreement just one day after NATO aircraft shot down four planes that had violated the UN-imposed no-fly zone over Bosnia. Karadzic declined to comment on the shoot-down Tuesday, saying that he lacked sufficient information.


Russia has carved a considerable role for itself in the peace effort in Bosnia over the past two weeks by playing on its ties with Serbia. Russian objections to a French plan to restore services to Sarajevo reportedly put it on hold Tuesday.


Citing U.N. sources, Reuters reported that Russia questioned language in the resolution that would place four more Bosnian towns under UN protection. Kozyrev also said Tuesday that he had spokenwith U.S. Secretary of State Warren Christopher the night before.


Christopher had said that the United States was engaged in talks with the parties, according to Kozyrev, who said he responded that such talks were insufficient on their own.