The blast, which occurred in the morning, slightly wounded a Croatian employee who was taken to hospital with injuries to his leg. The British ambassador, Sir John Ramsden, was not present at the time of the explosion. He told local media that he had not received any threats or warnings of an attack.
The explosion was condemned by the Croatian Prime Minister, Ivo Sanader, who said it was likely to have been an attack on the country's quest to become an EU member state.
"Although it is hard at the moment to speak about motives, I cannot help but think this act is directed against Croatia's efforts to join the EU," he said shortly after an emergency meeting with police and intelligence chiefs.
Opposition to EU accession has increased sharply since March, when entry talks were put on hold because of Britain's insistence that Zagreb surrender the former army commander Ante Gotovina to the international war crimes tribunal in The Hague.
The Croatian government claims that it does not know the whereabouts of General Gotovina, who is wanted for alleged wartime atrocities against Serbs in a 1995 offensive.
But Britain, which currentlu holds the EU presidency, is adamant that Croatia must extradite Gotovina, who has been in hiding since he was indicted in mid-2001, before accession talks can proceed.
Croatian nationalists oppose demands for Gotovina's arrest, and their opposition to Europe has gained support among the public. According to a recent survey, only 36 per cent of the population would like their country to join the EU.
"There are certainly people who want to slow down Croatia's integration into the EU," Mr Sanader said. "By this I do not mean Eurosceptics, which is a legitimate political position."
The Prime Minister added he was "determined" to find and punish those responsible for the attack.
Britain is to oversee a reassessment of Croatia's EU membership bid in forthcoming weeks.
Another "no" would deal a huge blow to Mr Sanader's 21-month-old reformist government, which has stepped up efforts to locate Gotovina in recent months.
A return of violence in Croatia would make EU talks even less likely than previously thought.
Zeljko Trkanjec, a political analyst, summed up the explosion as "the worst possible message, at the worst possible time".Reuse content