Boutros-Ghali issued the warning as he left Sarajevo without meeting Bosnian Serb leaders, who insisted cease-fire talks should be held on Serb-held territory.
Although there were no immediate plans to pull out the UN Protection Force (UNPROFOR) in Bosnia, the secretary-general said the warring factions had to show a readiness to negotiate and to cooperate with UN peacekeeping and relief efforts.
"My message to them is unless they do this it will be impossible for me to convince the Security Council to keep UNPROFOR here," he told reporters at the airport.
The UN Security Council would have to order any withdrawal of UN peacekeeping troops.
Boutros-Ghali met leaders of Bosnia's Moslem-led government amid jeers and whistling from a crowd of about 300 people, venting their bitterness over what they see as the UN's failure to protect civilians in Moslem enclaves under Serb assault.
As the UN chief completed his abortive trip to Sarajevo, U.S. Secretary of State Warren Christopher left for Europe on Wednesday with a new initiative which he hoped would heal a rift with the NATO allies over policy for the war-torn region. Christopher will attend a NATO foreign ministers meeting in Brussels and a Budapest summit of the Conference on Security and Cooperation in Europe during his trip.
The divisions among European countries and Washington have become more bitter as the Serb onslaught on Bihac has revealed the impotence of NATO and the UN.
Some European countries have accused the United States of sparking the attack on Bihac by its pro-Moslem policy, while some U.S. members of Congress charge that Britain and France have blocked a tough NATO response.
But on the eve of his departure for Brussels, Christopher unveiled a proposal to revive Bosnian peace talks that looked aimed at defusing the dispute with the allies who have long argued for diplomatic, rather than military, means to solve the conflict.
Christopher said he would put his proposal, for indirect talks between the Bosnian factions to be followed by a possible international conference, to a meeting of foreign ministers of the so-called "contact group" on Bosnia.
The ministers will meet Friday evening in Brussels at the end of the two-day NATO session.
However, while Washington was attempting to defuse the row between NATO and Europe, U.S. Senate Republican leader Robert Dole continued talking tough on the alliance's role ahead of talks with British Prime Minister John Major scheduled for Wednesday.
Dole called the UN's record of decision-making on Bosnia "abysmal" and called for an end to the arms embargo on the Bosnian government.
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