Unknown assailants tossed a grenade bomb at a police station in Somali capital, Mogadishu on Sunday night, witnesses said.

The attack too place at Howlwadag District police station and it caused unspecified number of casualties.

The police responded with fire after the exploration which was aimed to destabilise the capital, recovering from three decades of war.

There was immediate claim of responsibility for the bombing which becomes the second attack in two nights.

Al-Shabaab intensified attacks in Mogadishu since the government launched an offensive last night to liberate the country from the militants.

The security of the capital has been extremely tightened within additional NISA personnel deployed to main streets.

Last week, Al-Shabaab gunmen gained access to Mogadishu mayor's office, where at least 6 were killed in a six-hour siege.