SARAJEVO -- Russia on Tuesday poured cold water on a proposal by Secretary General Boutros Boutros-Ghali that UN troops should be pulled out of former Yugoslavia to make way for a force provided by the big powers.


Defense Minister Pavel Grachev said on a visit to Belgrade that only UN soldiers should act as peacekeepers and NATO was not a suitable replacement for the 35,000-strong UN force.


In Sarajevo, the Bosnian government said Boutros-Ghali's proposal would harm negotiations on a peace plan put forward by an international "contact group."


"It's quite surprising because in a way it prejudices the contact group decisions," Bosnian Prime Minister Haris Silajdzic told reporters.


The United Nations meanwhile reported a heavy exchange of artillery and mortar fire across the Serb-Moslem front line northwest of Maglaj in Bosnia, with 160 rounds recorded as landing in an hour.


The United Nations accused the Serbs of restricting its ability to investigate Serb violations of the UN-imposed heavy weapons exclusion zone around the Moslem enclave of Gorazde on Monday.


Grachev arrived in Belgrade accompanied by Russian special envoy Vitaly Churkin amid intense diplomatic efforts to persuade the Bosnian Serbs to reverse their rejection of the latest international peace plan.


The Yugoslav news agency Tanjug said it understood Grachev would propose to the Serbs that a Russian peacekeeping contingent be deployed around the northern Bosnian town of Brcko.


Brcko straddles an important Serb supply route whose status is of concern to the Serbs in the event of a division of Bosnia along the lines proposed by the five-power contact group.


The peace plan, which the Serbs have so far rejected, awards 51 percent of Bosnia to the Moslem-Croat alliance and the rest to the Serbs, who now hold 70 percent.


The "northern corridor," which runs through a bottleneck around Brcko, links Serbia proper with Serb-held territory in western Bosnia and Croatia.


Grachev also said he wanted to give Russia's reaction to Boutros-Ghali's suggestion that the UN protection force, UNPROFOR, should be pulled out whether a peace settlement is reached or not. "I came here to convey Russia's stand on Boutros-Ghali's statement that UNPROFOR should be replaced by NATO. The UN Security Council is now in a state of shock," Grachev told reporters.


"NATO is not a peacekeeping organization. Only UNPROFOR can fulfil the mission in Bosnia."


Boutros-Ghali suggested Monday in a letter to the Security Council that only major powers such as the United States, not the lightly armed and dangerously exposed UN force, could enforce a peace deal.


Boutros-Ghali did not mention NATO in his letter, but he said the contact group -- the United States, Britain, France, Germany and Russia -- should provide forces to back up their peace proposals. Of the contact group, only Russia is not a NATO member.


Grachev was scheduled to hold talks with Serbian President Slobodan Milosevic, Yugoslav army commanders and later with Bosnian Serb leader Radovan Karadzic and Bosnian Serb army commander Ratko Mladic. He said he would also visit Russian UN peacekeeping troops in former Yugoslavia.


In Sarajevo, a senior UN official gave a warning that UN operations in key areas of Bosnia could grind to a halt unless a dispute over Serb prisoners and Moslem missing persons was resolved in the next few days.


The Serbs have threatened to block UN movements on their territory unless the Moslems release a group of Serb prisoners. The Moslems say they will not do so until the Serbs account for a group of Moslems who disappeared after being abducted by the Serbs two years ago.


"We are making no progress on this problem," said Viktor Andreev, UN head of civil affairs in Bosnia. "Mladic says if there is no solution soon he will halt all cooperation with the United Nations.