High-ranking diplomats from Russia, the United States, Britain, Germany and France met in closed session Monday to discuss the Bosnian Serbs' rejection of the latest plan for ending the war in Bosnia.


European Union and UN representatives also attended the talks, held at an undisclosed location in Moscow, a Foreign Ministry spokesman said.


Bosnia's Moslem government has accepted the plan, which would give 51 percent of Bosnia to a Moslem-Croat federation and 49 percent to the Serbs, who now control about 70 percent. But the Serbs insisted on further negotiations, which U.S. officials described as tantamount to a rejection.


The five nations meeting Monday drafted the plan. They had threatened to tighten sanctions on Serbia proper and ease an arms embargo on Moslems if the Bosnian Serbs rejected the proposal.


Russian Deputy Foreign Minister Igor Ivanov told Itar-Tass that the collapse of the peace plan could have catastrophic consequences. He said the five-nation contact group was studying additional measures Monday to implement the plan to divide Bosnia-Herzegovina.


He called the offer "a balanced plan that reflects the interests of all the sides."


Interfax said the group was looking at the Bosnian Serbs' "vague response" to the plan and would set the agenda for the next ministerial-level meeting on Bosnia, to be held in Geneva on Saturday.


Russia, a traditional Serb ally, is seen as the best hope for getting the plan accepted.


Differences in the contact group now meeting in Moscow have previously arisen between the four Western partners and Russia over Moscow's apparently more sympathetic approach to the Serbs' reaction.


Interfax said President Boris Yeltsin's envoy to Yugoslavia, Vitaly Churkin, was representing Russia at Monday's talks.


On Saturday, Churkin told Interfax: "The response of the Bosnian Serbs, to put it mildly, can't satisfy us to the fullest extent."


He said the international community was continuing to work with the Bosnian Serbs "so that their final answer would be more sensible and definite."


Russian Defense Minister Pavel Grachev was to travel to Belgrade on Tuesday to meet with "presidents and military ministers" in the former Yugoslavia, Itar-Tass reported.


Grachev planned to meet with Serbian President Slobodan Milosevic, Bosnian Serb leader Radovan Karadzic, Bosnian Serb army commander Ratko Mladic, and others, the news agency said. It also said he would visit Russian peacekeepers near the Croatian city of Vukovar.