An explosion near a Turkish police bus wounded 10 people, including three police officers, in central Istanbul early Thursday, Anatolia news agency reported citing official sources. The blast hit close to the offices of the ruling Justice and Development Party (AKP), said the private NTV news channel. Reports said that the explosion was believed to have been caused by a bomb. Witnesses spoke of a strong blast, possibly from explosives carried on a motorcycle, NTV said. The wounded policemen were hospitalized with minor injuries. Police blocked access to the blast zone, fearing a second explosion. Several outlawed armed groups -- Kurdish, Islamist and leftist extremist -- have carried out bomb attacks in Istanbul in the past. Last September a powerful bomb rocked the centre of the capital Ankara, killing three people and wounding at least 15.