Three persons were killed as six unidentified gunmen made an unsucessful bid on the life of former legislator from Chittoor C K Babu, police said in Tirupati on Friday.

The former Congress MLA escaped unhurt in the attack at his office in Chittoor, about 70 km from Tirupati, on Friday morning, they said.

Babu's security guard retaliated when the heavily armed attackers opened fire, they said adding, those killed included the security guard and an attacker.

Tension prevailed in Chittoor and additional forces have been rushed to the town following the incident, they said.