A car bomb has exploded in the heart of the Somali capital Mogadishu, injuring two people and prompting police to open retaliatory fire.Police said four suspects had been detained after the explosion in the city's busy administrative district."A car bomb has just exploded in Maka al Mukarram road. Then the police opened fire," resident Hussein Omar told the Reuters news agency."We got a man with a remote control seconds after he detonated the car. We also arrested three other suspects," police spokesperson Abudullahi Barise said.No one claimed responsibility for the attack in the immediate aftermath, but suspicion is likely to fall on the al-Shabaab armed group.There has been a surge in suicide bombings and remotely detonated blasts in Mogadishu since al-Shabaab pulled most of its fighters out of the coastal city, vowing to turn increasingly to al-Qaeda-inspired tactics.