Three persons were injured when a powerful timer bomb exploded in the high-security office of the Manipur Public Works department here on Wednesday.

The bomb smashed window panes and damaged doors during peak office hour, police said.

All the injured were admitted to hospital.

The building has been heavily fortified by securitymen after government officials faced frequent extortion demands by various militant outfits.

"It was a very powerful timer bomb," said Additional Director General of Police V. Jathang who along with DGF Y. Joykumar visited the spot soon after the explosion.