Blast at Istanbul police station kills one: agency ISTANBUL (Reuters) - An explosion at a police station in a suburb of Turkey's biggest city Istanbul on Tuesday killed one person and wounded at least three others, the local Dogan news agency reported. Television footage showed damage to the front doors of the police station in Sultangazi, a working class and largely residential district on the northern edge of central Istanbul. The cause of the blast was not known but Turkish television stations said there were rumors a suicide bomber carried out the blast. There was no independent confirmation of this. The main domestic security threat in Turkey comes from the separatist Kurdistan Workers Party (PKK), considered a terrorist group by the United States, European Union and Turkey. But the PKK has focused its campaign largely on targets in the mainly Kurdish southeast. Far-left groups and Islamic radicals have also carried out attacks in Istanbul in the past. Reporting by Ayla Jean Yackley and Ece Toksabay; Writing by Nick Tattersall; editing by Mark Heinrich