Early soundings in the Serb-controlled areas indicated an overwhelming 'no' vote for the plan, which would divide Bosnia into 10 semi-autonomous regions.
Thousands of people braved sniper fire in Serb-held neighbourhoods of Sarajevo to vote at polling places that opened and shut as the firing flared and subsided.
Radovan Karadzic, the Bosnian Serb leader, said last night that the current United Nations-backed peace plan was now defunct. 'Vance-Owen is dead and gone,' Mr Karadzic said. He stated his support for a new peace plan that he said was being formulated by the former Soviet president Mikhail Gorbachev and Henry Kissinger, the former US Secretary of State.
'Kissinger is right. Create three states. That is the reality,' he said.
In Moscow, however, Andrei Kozyrev, the Russian Foreign Minister, yesterday reaffirmed his country's support for the Vance-Owen plan and repeated an offer to send a force of border monitors. Mr Kozyrev said it was important to begin gradually implementing the Vance-Owen plan regardless of the outcome of the referendum.
'The Vance-Owen plan has been approved by everybody and I don't believe we have to wait until the last fighter says that Bosnia approves the plan,' Mr Kozyrev said.
Intelligence experts believe the latest fighting has begun because all sides believe a peace plan of some kind - either Vance-Owen or a division of Bosnia into three areas reflecting the status quo achieved by fighting - is imminent. Croats and Serbs have gained almost all they want, apart from 'minor adjustments' such as a northern corridor linking Serb territory.
In the southern Bosnian town of Mostar, Bosnian Croat artillery and multiple rocket launchers again pounded targets, with a company of 60 men from the Spanish UN battalion coming under fire.
For several days columns of refugees have been seen leaving the city. Yesterday a brief ceasefire was agreed so that humanitarian convoys could move in. Fighting then resumed to crush the last remnants of Muslim resistance. 'They're kicking shit out of them', said one UN source. 'They don't believe in 'minimum force'.'
The UN Protection Force last night said Bosnia's President, Alija Izetbegovic, the Croatian President, Franjo Tudjman, the Bosnian Croat leader, Mate Boban, and the EC mediator, Lord Owen, would meet in Mostar tomorrow to try to negotiate an end to the Muslim-Croat conflict.
Heavy fighting has continued in the north-east, around and in the town of Brcko, where Bosnian Serbs are trying to enlarge the crucial Posavina corridor linking Serbia and eastern Bosnia with Serb-held areas to the west.
In this region Croats and Muslims are fighting together against the Serbs, but are reported to be retreating south. If the Serbs continue their drive, 40,000 more refugees are expected to stream into the Muslim-held town of Tuzla.
In Sarajevo, Serbian and Croatian commanders signed a new ceasefire agreement that will cover all of Bosnia from noon (10.00 GMT) tomorrow.
'This will be the best-written ceasefire document ever violated,' a UN observer said.
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