Police said the man walked into the office wearing a helmet and poured and set afire the solution, suspected to be petroleum or kerosene.
In the ensuing melee six persons, five of them office staff, suffered injuries, including burns.
Police ruled out the presence of any explosive material at the site.
Office staff including village officer Mohanan N (51), Krishna Kumar B (43), Vengopal (45), Prabhakaran Nair (43) and Vijayamma and one Isahab (78), who had come to pay his land tax, were among those who suffered injuries.
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"We can arrive at a conclusion about the solution used by the person only after a detailed examination. But as per the primary evidence so far, there is no presence of any explosive materials at the site," he told PTI.
A team of police officers are investigating the case under the direct supervision of rural Superintendent of Police P Shafeen Ahmed.
Meanwhile, the injured are recovering at various hospitals, including the Medical College Hospital here.