Three loud explosions, followed by mushroom clouds rising from the Bosnian Serb barracks at Lukavica, south of Sarajevo, marked the renewal of Nato's air campaign against the rebels yesterday - punishment for their failure to withdraw artillery from the city.
Amid UN reports on the situation and contradictory signals from Bosnian Serb leaders,some observers felt a sense of deja vu. It seemed to be a re-run of February 1994, in which a massacre in a market place was followed by a Nato ultimatum to pull out weapons and open up roads into the the city.
Then the Serbs took a timorous world to the brink, used a Russian diplomat as cover for semi-compliance, outplayed the alliance and reaped the rewards. But times have changed.
"I think the historical precedent is well-known by the [UN and Nato] commanders," said Lieutenant-Colonel Chris Vernon, a UN spokesman in Sarajevo. "They are well aware of the negotiating and Machiavellian skills of the Bosnian Serbs in this respect and it is a factor in decision-making."
Sarajevans, inured to disappointment, were sceptical of Western resolve. As air raid sirens wailed at lunch-time, residents ignored the warnings. Minutes later Nato jets thundered above the city, attacking Lukavica barracks and targets closer to Serb headquarters in Pale, east of Sarajevo.
From a vantage point in the city centre smoke could be seen rising from behind a hill masking Lukavica - and beyond it the huge Bosnian flag planted on Mount Igman, west of the city.
Heavy artillery of the multi-national Rapid Reaction Force deployed on Mt Igman opened fire several times, the explosions rumbling across the valley, but only in response to Serb attacks, UN officials said. Two British Warrior vehicles opened fire on a Bosnian Serb mortar position in Hadzici, west of the city, "because of a perceived threat", a spokeswoman said.
Reporters in Pale heard jets screaming overhead, followed by distant explosions in the mountains, but said there were no signs of panic. Life may not be so easy for Serbs living closer to the targets around Sarajevo. One report said Ratko Mladic, the Bosnian Serb commander, was willing to pull out weapons and replace them with infantry, but the suggestion was interpreted as an attempt to stop civilians leaving the area.
Gen Mladic's response to Nato's latest warning came in an intemperate letter refusing the UN demands, except on conditions already rejected by the Western alliance. It was faxed to UN headquarters hours after President Slobodan Milosevic of Serbia as well as the Bosnian Serb leader, Radovan Karadzic and his "vice-president" pledged compliance.
It was not the kind of rhetoric to win any friends at Nato, who have lost patience with the games played by the Bosnian Serbs. One source said: "Mladic was nowhere to be seen and then he gave us this real long letter, coming in at the 11th hour with a letter in Cyrillic, five-and- a-half-pages long in English, which, when you finally pore over it, says nothing."
Nato reconnaissance flights detected movement of heavy weapons around Sarajevo on Monday, but concluded that as no tanks or heavy guns had been moved out of the exclusion zone, there was no compliance with the demands. "We really did try to give them the benefit of the doubt," the Nato source said. This time the peace-keepers were not willing to give an inch. A source said: "It's hard-line, actually, for once."