The UN reported more than 400 artillery rounds near Visoko, Breza and Ilijas, north of Sarajevo, but an official said fighting subsided after the General's warning.
Claire Grimes, a UN spokeswoman in Sarajevo, said that General Rose had written to the Bosnian Serb commander in the region and the Bosnian Vice-President, Ejup Ganic, to say that 'serious breaches of the total exclusion zone' had been reported.
The UN, he said, 'would use all available means to deter these attacks', which, Ms Grimes said, could include air strikes. The UN warning was seen less as a serious threat to bomb the Muslims than as a signal to the Bosnian Serbs that the UN was trying to maintain its impartiality.
Another spokesman, Major Rob Annink, said UN troops deployed in the area had seen a tank in the zone but did not know which side it belonged to.
The Serbs were also told to remove three heavy weapons from the exclusion zone around the Muslim enclave of Gorazde. Major Annink said peace-keepers had counted 20 detonations, apparently from shells fired by the renegade weapons, but added that they did not pose a threat to the town of Gorazde, about 10 miles away.
North of Sarajevo, the Bosnian army is apparently trying to take land from the Serbs along the road from Sarajevo to Tuzla via Olovo, and it has had some success in winning ground south of Vares from the Serbs. The UN, said one official, 'is not in the business of stopping them fighting per se', but is concerned to keep out of the zone weapons that could threaten Sarajevo. It is also trying to prop up a two-month old agreement to suspend offensive actions.
Yasushi Akashi, the senior UN official in the former Yugoslavia, appealed to both sides 'at this critical juncture . . . to show utmost military restraint'. But his plea is likely to fall on deaf ears in Sarajevo, which is encouraged by the apparent breach between Belgrade and the Bosnian Serbs.
Buoyed by its military success against Muslim rebels in Bihac and by the Bosnian Serbs' dispute with Serbia, the Bosnian government army is in no mood to hold its fire. The Bosnian army appears to be advancing on Velika Kladusa, the heart of the rebellious fiefdom ruled by Fikret Abdic. The wealthy businessman broke with the Sarajevo government last year and signed a deal with the Bosnian Serbs.
Despite having lost his best commander and several towns to the advancing Bosnian army, Mr Abdic yesterday insisted he was 'unbeatable' and rejected an amnesty offered by the Bosnian government. 'It is impossible to part me from my people,' he said in a telephone interview from his renovated castle in Velika Kladusa.
He said that refugees and soldiers who had escaped the Bosnian army advance, by fleeing west into Serb-held areas of Croatia, had crossed back into Kladusa. The UN put the number moving across at 1,400. The UN described the situation in Velika Kladusa as 'fairly calm', adding that there was 'no reason to believe they face any immediate threat'.
Mr Abdic said that he had offered to negotiate a deal with Sarajevo but that the Bosnian government turned him down. Sergio Vieira de Mello, a senior UN official, went to Bihac yesterday to mediate between the two sides.
In Sarajevo the UN cancelled helicopter flights after a British Sea King taking off from the airport was hit by a small-arms round. There were no casualties and the helicopter later left as planned for Kiseljak. The city was relatively quiet, although the UN reported a slight increase in ceasefire violations.