Several foreigners were among the wounded in the blasts late on Sunday at three locations in Songkhla province: the Hat Yai airport that serves as the main gateway to Thailand's far south, a department store and a hotel.
They were the first major attacks outside of Thailand's three southernmost provinces where a Muslim insurgency has raged since early last year, claiming almost 800 lives.
Songkhla is just north of that region.
"We have to check the security at all airports and railway stations in southern Thailand," the Deputy Minister of Transport and Communications Phumtham Wechayachai said on Monday.
Store, hotel hit
The explosion at the Hat Yai airport killed two people, Songkhla Governor Somporn Chaibongyang said. Another bomb exploded at the city's Carrefour department store, Somporn and other officials said.
A third bomb exploded in front of a hotel in the city of Songkhla, on the Gulf of Thailand coast not far from Hat Yai.
Hat Yai's police chief, Col Supasin Issarakul na Ayutthaya, said 35 people were injured in the blasts, but the government's Radio Thailand reported that 65 had suffered wounds, with a number of them in serious or critical condition.
The injured included a British woman, a French woman, two people from Malaysia and two from Brunei, Supasin and hospital officials said.
Triggered by phone
Initial investigations showed that the blasts were triggered by mobile telephone signals, military spokesman Lt-Gen Palangoon Kraharn said.
Television footage showed dazed and bloodied people at Hat Yai airport being treated by paramedics.
The airport bomb had been left in a bag by an unidentified man in the waiting area, Gen Chaiyasit Shinawatra, the Thai military supreme commander, said.
The bomb at the Dream World Hotel was hidden in a motorcycle, police said.
All three explosions took place between 8pm and 8.30pm (1300 GMT and 1330 GMT), officials said.
No one claimed responsibility for the blasts, but they were thought to be linked to the insurgency in Thailand's Muslim-dominated southernmost provinces.
The bombings were the first major attacks outside the provinces of Narathiwat, Yala and Pattani, where shootings or small bombings have occurred almost daily since January 2004.