A group of armed ultras, including women, stormed into Padia, about 70 km from here, in the early hours and entered the block office building after breaking the lock, Malkangiri Superintendent of Police Akhileswar Singh said.
The red rebels set the building on fire before triggering a powerful blast, causing extensive damage to the structure, he said, adding no one was harmed in the attack.
Four of the five rooms in the building with asbestos roof were completely destroyed in the blast which damaged volumes of documents and important records, gram panchayat officer Basant Behera said.
The SP said the attack was a desperate attempt by the Maoists to counter stepped up anti-naxal operations mounted by the security forces in the region.
A poster found from the site stated that the attack was in protest against an encounter with security forces in September this year in which around 13 Maoists had been killed, police said, adding the poster also sought a halt to anti-naxal operation and withdrawal of BSF from the region.
Maoists had blown up the new building of Padia block office in September, 2010, following which work was being done from the old building which now got destroyed in the pre-dawn attack, sources said.