A man walks past a picture of Thailand's late King Bhumibol Adulyadej during the mourning period, outside a shopping mall in Bangkok, Thailand January 20, 2017. REUTERS/Chaiwat Subprasom

BANGKOK (Reuters) - Police in Thailand said on Saturday they have arrested five people for allegedly setting fire to portraits of late King Bhumibol Adulyadej who died last year.

The death of the revered king after seven decades on the throne plunged the Southeast Asian country into mourning and heightened sensitivities to any negative comment.

Criticism of the monarch, the regent and the heir, known by the French term lese majeste, is a crime that carries a jail sentence of up to 15 years in Thailand.

The suspects, four men and a boy, were arrested on Friday, police in the northeastern province of Khon Kaen, police said.

“The case is being processed and under investigation at this time,” a Khon Kaen police officer said.

All five are in custody and have been transferred to the 11th Army Circle base in Bangkok, a facility the military uses as a temporary prison.

King Maha Vajiralongkorn, 64, ascended the throne in December following the death of his father, King Bhumibol, in October.

Thailand is observing a year of mourning for King Bhumibol, who was seen as semi-divine by many people.