A man and his daughter were among the dead. Two others were pensioners. Police said at least 50 to 60 houses were destroyed or damaged.
Speaking in Brussels, a Nato spokesman, Air Commodore David Wilby, blamed a technical fault and promised an investigation. "It is possible that one of our weapons fell short of the target," he said. "Despite our meticulous and careful pre-attack planning, the law of statistics will at some stage go against us. Whatever the reason, any unintended damage to civilian property or loss of life is very much regretted."
Nato bombers targeted Aleksinac, 120 miles south of Belgrade, as it is the headquarters of the Yugoslav Army's 203rd Mixed Artillery Brigade. But local residents said the alliance had no excuse for targeting the centre of town. "The army barracks are a mile away," said Suzana Turk, who had been next-door to a house which took a direct hit.
The Secretary of State for Defence, George Robertson, said the bombing of Aleksinac was "regrettable" but insisted some casualties and errors were inevitable in a campaign of this size. He also accused the Serbian authorities of wantonly increasing the risk to their own population by hiding military assets in residential areas, schools and factories. He said the the Serbs were doing this to evade detection and bombing by Nato missiles.