More than 1,000 Muslims, mainly women, assembled near the lorries after they crossed Bosnian Serb lines into the town early in the morning, only to be ordered home by police.
The authorities in Srebrenica said they knew the evacuation plan had been approved by Bosnia's Muslim President, Alija Izetbegovic, but said his word would make no difference.
They said the UN was reneging on a promise by General Philippe Morillon, the UN force commander in Bosnia, to place the town under UN protection and save the local population of about 60,000, now living in appalling conditions, from further Bosnian Serb attacks.
The UN had planned to send 20 lorries a day into Srebrenica, leave food in the town and take about 1,500 people a day out to Tuzla. In private they said the aim was to get as many civilians as possible out before the town fell to the Serbs and people were massacred.
Officials in Belgrade said the UN would try again to bring out the people tomorrow. Others in Sarajevo said the UN would evacuate only refugees and leave the town's inhabitants behind, to avoid accusations of helping in ethnic cleansing.
There is no mistaking Serbian determination to take the town and stamp out one of the last remaining Muslim pockets in eastern Bosnia. The nearest Serbian positions are about two miles from the town centre, and the advance seems remorseless.
The UN said earlier it would place a company of 150 troops and military observers in Srebrenica, but its resolve crumbled when faced with the Bosnian Serbs' determination to have the town - and soon.
UN-brokered peace talks between the military leaders of the three communities in Bosnia, due to take place yesterday at Sarajevo airport, failed to take place. Journalists were ferried to the airport through devastated lifeless suburbs in spanking white UN armoured cars for what was billed as a breakthough, but none of the leading players showed up.
Sefer Halilovic, chief of the Muslim-led army of Bosnia-Herzegovina, instead sent a statement making Serbian adherence to an earlier ceasefire agreement the condition of his attendance.
In Geneva, the UN Children's Fund said 3,000 children had been killed in Sarajevo since the Bosnian war broke out a year ago, In a report issued to mark the first year of the war, Unicef said 40 per cent of the children had been shot by snipers.
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