At least 10 people have been killed in three explosions in the southern Thai province of Yala.
The blasts occurred this morning in the commercial district of Yala city.
It is reported that two of the bombs were hidden in motorcycles and the third in a car.
Thailand's three southernmost provinces have been plagued by bomb attacks and shootings since 2004, when a separatist campaign reignited.
In an apparent escalation of their tactics, suspected militants have now attacked a hotel in Hat Yai, the largest city in southern Thailand and a popular destination for tourists from neighbouring Malaysia and Singapore.
A car bomb in the basement triggered a fire which spread to a shopping mall within the Lee Gardens Plaza Hotel and killed three people, including a Malaysian tourist, according to the police.
Songkhla provincial governor Grisada Boorach said 416 people were injured, mostly suffering from smoke inhalation, and 140 were still in hospital.
Until now Hat Yai and Songkhla province have been relatively untouched by the insurgency that has claimed thousands of lives in the neighbouring Muslim-dominated provinces of Yala, Pattani and Narathiwat since 2004.
"There is no hint why they did this at this time," Hat Yai police chief Colonel Khomgrit Srisong told AFP by telephone. "We're questioning witnesses and the injured for more information."
The hotel bombing came about an hour after two car bombs minutes apart hit the town of Yala around midday as people were out shopping.
Prime Minister Yingluck Shinawatra said the security forces knew which group was responsible but she would not say in order to let them do their job.
