UN spokesman Alex Ivanko said the authorities assumed the blast was a car bomb. "There hasn't been a blast like this really since Dayton," said Liam McDowall, a UN spokesman in Sarajevo.
A Mostar hospital said 30 people were treated for injuries and three of them were in a serious condition. A man was paralysed from the waist down and had to be evacuated by Nato helicopter for emergency treatment in Croatia, said Dr Zoran Antunovic, the surgeon on duty at the time. "He was buried under a wall that collapsed due to the explosion," Dr Antunovic said. Three children - including a one-month-old baby - were among those who suffered lesser injuries from flying debris and glass.
The bomb is the latest event in simmering tensions between the Croat and Moslem communities in Mostar. Tensions were already high after Croat leaders came close to boycotting municipal elections held last weekend. And Moslem leaders expressed anger this week when Croat officials said they might renege on a promise to drop plans to unify three predominantly Croat districts in western Mostar.
Moslems and Croats fought a 10-month war in 1993-94 that devastated the city and left it divided into Moslem and Croat sectors. The two sides renewed a military alliance against the Serbs in 1994 and formed a federation covering half of Bosnia but relations in Mostar remain tense.
Despite millions of dollars in reconstruction aid and three years of diplomatic efforts aimed at reunifying the town, Mostar is still strictly partitioned along ethnic lines.
The police station was run by the joint Muslim-Croat police force established in July after months of arduous negotiation. "I think that this was an attack against the joint police in Mostar," said Sefkija Dziho, the Muslims' deputy minister for internal affairs in the region.
A spokesman for the international community's High Representative to Bosnia condemned the blast: "This was a senseless attack with a clear aim to destabilise the situation in the city at what is an extremely sensitive time."
UN spokesman Ivanko said: "It is extremely disturbing that almost two years after the signing of the Dayton peace agreement certain individuals continue to use barbaric tactics to get their point across."