A car bomb has been detonated at the gate of the police headquarters in Lashkar Gah. Ten police officers died in the attack. A child was also killed.
Twelve people are said to have been injured.
Responsibility for security in the southern Afghan city was recently handed back to Afghan forces as part of the transfer of control from the NATO-led ISAF.
Lashkar Gah is the regional capital of the turbulent province of Helmand – which continues to be a flashpoint of the insurgency.
The Taliban has admitted it was behind the attack, the latest in a recent series of high-profile Taliban raids.