An exiled Thai critic of the country's military and monarchy said he was attacked in his home in Japan last month and believes Thai authorities were behind the incident, an accusation that was ridiculed by the kingdom's army chief.

Pavin Chachavalpongpun, a 48-year-old associate professor at Kyoto University, said he was asleep with his partner when a man broke into their home last month at about 4 a.m. and sprayed the couple with a substance that burned their skin.

Neither was seriously hurt, but Pavin said they have been told by police not to return home. The police confirmed they were investigating a July 8 incident in which a Thai man was sprayed in his house.