SARAJEVO: The first day of a cease-fire brought calm to Sarajevo and much of Bosnia yesterday, but continuing fighting in the northwest threatened to wreck the truce. Each side accused the other of mounting large-scale attacks after the midnight deadline, but in other parts of Bosnia only sporadic shooting was reported. Bosnia's Muslim President Alija Izetbegovic said in Vienna that the Serbs had launched a counter-attack to recapture the town of Sanski Most, taken by the government side hours before the truce deadline. 'I think that this news is really putting at stake the cease-fire and the agreement. We will have to respond to it if it does not stop,' he said. The United Nations has no presence near the northwestern frontlines. Bosnian Serb military commander Ratko Mladic sent a formal letter of protest to UN forces. 'It is obvious the Muslim side does not respect any cease-fire agreement and seriously threatens the peace process and provokes wide-scale conflict,' it said, calling on the UN and the major powers to ensure the truce was respected. Serb military authorities in turn accused Muslim troops of mounting 'heavy attacks' near Sanski Most and Bosanska Krupa to its northwest. Serb forces accused government Muslim troops of engaging in sporadic shooting across battlelines and of small-arms fire into Serb areas of Sarajevo in the first hour after midnight. A single missile fired about two hours after the deadline hit an apartment block in Sarajevo. UN spokesman Lieutenant-Colonel Chris Vernon said in Sarajevo there had been a 'considerable decrease' in fighting. 'Militarily it is unrealistic to expect that any two armies along a 1,000 kilometre confrontation line who have been in close contact are going to be able to disengage themselves within a few hours,' he said. 'People who have been fighting each other at a distance of 200 metres don't just put their rifles in the air and say 'I'm walking backwards, thank you very much'. ' Sarajevans strolled freely on the streets of the Bosnian capital after daylight, apparently safe from gunfire. But a UN convoy was forced to abandon an attempt to carry aid from Sarajevo to the besieged enclave of Gorazde because of mines and landslides on the long-closed route. Bosnian government and Serb officials met at Sarajevo airport yesterday for the first meeting of the Joint Commission on the cease-fire. They discussed ways of monitoring the truce, including defining the confrontation line. 'The parties co-operated well,' Colonel Vernon said afterwards. In The Hague, Muslim survivors of Serb prison camps told the UN war crimes tribunal how neighbour turned on neighbour amid a nightmare of torture and killings early in the war. 'Things changed overnight. It was as if we had not lived together at all, even though we had lived together for centuries,' said Suad Mahmutovic, the ninth witness to testify. The 41-year-old was giving evidence on the fourth day of hearings into the case of Bosnian Serb Dragan Nikolic, who commanded the Susica camp in northeastern Bosnia in 1992 and is accused of murder, torture and crimes against humanity. Nikolic is believed to be in Serb-held Bosnia. In Zagreb, UN human rights envoy Elisabeth Rehn urged Croatia yesterday to improve its observance of human rights - recently tarnished by anti-Serb atrocities - if it wanted to be considered part of Europe. In Brussels, Bosnian government leaders sought help from the European Union to rebuild their shattered country. 'I think Bosnian reconstruction should start now,' Bosnian Prime Minister Haris Silajdzic said.