Andhra Pradesh police chief S.R. Sukumara told AFP that a high-level inquiry would probe how guerrillas belonging to the banned People's War Group (PWG) breached Chief Minister N. Chandrababu Naidu's highest category security.

"Though there are no claims so far the nature of the attack and the use of Claymore mines point a finger at the PWG," said Sukumara.

"The probe will not spare either the culprits or security officials," he warned.

Naidu had a narrow escape when mines exploded Wednesday blasting his bullet-proof Ambassador car on a forest road between Hindu temples at Tirupati and Tirumala, but four others were in serious condition.

While Naidu has injured his right collarbone, the four seriously injured are state cabinet minister Gopalakrishna Reddy, two state legislators from Naidu's party and his driver, a party official said.

Gautam Sawang, head of the state police's intelligence, said a PWG bombing expert known as Sudhakar may have masterminded the daring attack on Naidu's convoy.

"This operation was probably carried out by a special unit of the PWG. We suspect the team could have been led by top PWG leader Sudhakar who had recently shifted his operations to the Chittor forest area where the attack took place," said Sawang.

Naidu's own regional Telugu Desam Party flayed the police for failing to protect its leader.

"It is shocking that the PWG got so close to the chief minister. The police know that he is on the PWG hit list. They should have taken more precautions," said R. Chandrashekhar Reddy, a leader of the TDP.

Activists of Naidu's party took to the streets on Wednesday and smashed windscreens of buses to protest the assassination attempt.

Naidu's government had opened negotiations in June last year with Maoist rebels to end a three-decade insurgency in which about 10,000 people have died.

However, a Maoist attack during peace talks on a police bus in Andhra Pradesh derailed the move.