Red Shirt campaigners in the region have defied a state of emergency that has been declared in 23 provinces as well as the capital Bangkok following weeks of unrest and deadly violence.
"Fire gutted four provincial halls almost simultaneously... including in Udon Thani, Khon Kaen, Mukdahan and Ubon Ratchthani," said Manit Wattansen, permanent secretary at the interior ministry.
The arson attacks came as dawn revealed smouldering buildings, looted shops and at least nine dead bodies in Bangkok, a day after the country's military cracked down on protesters who had occupied parts of the city's commercial area for weeks.
The halls, which were seriously damaged in the attacks, house the offices of the provincial governors as well as agencies like taxation and education.
Protest camp stormed by military
"Authorities can control the situation to some extent, but there are still protests in Lampang and Chiang Mai," Manit said, referring to northern towns popular with tourists.
Army spokesman Sunsern Kaewkumnerd said that 13,000 Red Shirt protesters rallied in 20 provinces on Wednesday night after their protest camp in Bangkok was stormed by armed forces.
The gatherings went ahead despite the curfew announced after enraged protesters went on the rampage in the capital after their rally base was shut down in an army offensive.
The provinces are mostly in the protesters' heartland in the north and northeast of the kingdom, which has a total of 76 provinces.
There are fears that the overwhelming offensive against the Reds, who had occupied Bangkok's main shopping district for six weeks, will trigger trouble in the rest of the country.
Arson, grenade attacks in Chiang Mai
Pairoj Saengpoowong, a deputy governor of Chiang Mai province, said the Red Shirts had also carried out an arson attack on another deputy's house.
"They set fire to two fire trucks last night and mounted small grenade attacks to cause disturbances," he said.
Pairoj said that on Thursday provincial authorities strictly banned any gatherings or actions to incite unrest, and that the situation had quietened with protest leaders going into hiding.
"It's a continuous reaction to the dispersal in Bangkok and I don't think it will last long," he said.
Thailand is largely split between the Reds, whose supporters are mainly rural and urban poor, and the rival Yellows, who are pro-establishment and detest the Reds' hero, ex-premier Thaksin Shinawatra, who was ousted in a 2006 coup.
