NEW DELHI (AFP) - A bomb explosion at a court killed at least two people and left more than a dozen injured in the eastern Indian state of Bihar on Friday, television channels reported.

The explosion comes amid tightened security across India ahead of the arrival of US President Barack Obama for a three-day visit on Sunday.

According to reports, the bomber was a woman who blew herself up, killing herself and a policeman, outside a court. "I can confirm that two people have died and around half a dozen are injured with splinter injuries," Gupteshwar Pandey, the additional director general of police in Bihar, told AFP.

A senior police officer said that there was no reason to suspect the explosion was the work of militant groups and it was thought the device went off prematurely.

CNN-IBN television network said that the woman's body had been blown to pieces, adding that seven people had so far been admitted to a nearby hospital after the explosion at a civil court in Bihar's Bhojpur district.

The local police chief said that the blast occurred around noon as a prison van arrived at the court.

The blast happened at 11:30 am (2 pm Singapore time) at the civil court. "The woman and a police constable died on the spot," Amrendra Kumar Ambedkar, inspector general of police, told AFP. "One policewoman is in a critical condition, along with 16 other people," he added by phone from the state capital Patna.

Mr Ambedkar said two prisoners, who were attending a hearing, had managed to escape after the explosion, adding that both men had staged unsuccessful attempts to escape while in pre-trial detention.

"The two prisoners escaped following the blast. We suspect the blast was carried out to free them," he said. "As of now we don't see any terror angle."

Indian security forces have been on a general heightened state of alert ahead of the three-day visit by Obama who is due to spend time in the capital New Delhi and the northern city of Agra, home to the Taj Mahal.