Maoists late on Friday night attacked a police station in Andhra Pradesh's Nalgonda district, killing four policemen.

Following the attack on Atmakur police station, the police have sounded a red alert in Hyderabad as well as the Maoist-affected districts.

The attack in state Home Minister K Jana Reddy's district comes nearly four weeks after the killing of Maoist committee secretary Madhav and seven other Maoists by the police in an encounter in Nallamala forests on July 23.

According to sources, a group of around 10 Maoists stormed the police station, and exploded a bomb. The police station was plunged into darkness as the power supply was cut. As the police personnel started running for cover, the Maoists caught hold of four of them.

They then tied the cops to a tree in the police station compound and shot them dead at point blank range. The dead have been identified as Sub-inspector Chand Pasha, Assistant Sub-Inspector Sultan Moinuddin, Constable Karim and Home Guard Lingamaiah. Four other policemen also sustained bullet injuries.

The timing of the attack also coincides with the renewal of the ban on CPI-Maoist and six of its frontal organizations for another year effective from August 17.