(CNN) -- A series of deadly car bombings in two southern Thai provinces over the weekend are linked, officials said Sunday.
The blasts, in Songkhla and Yala provinces on Saturday, killed 13 people and injured more than 500, according to CNN affiliate MCOT.
The first two blasts took place in Yala when bombs stashed in stolen trucks went off, police said.
The blasts set fires to nearby vehicles and buildings, Police Lt. Gen. Paitoon Chuchaiya told CNN affiliate MCOT.
The attacks killed 10 people and injured 100, authorities said.
About an hour later, another car bomb exploded in the underground parking of Lee Gardens Plaza Hotel in nearby Songkhla province. It killed three and injured 400, according to MCOT.
Thai Prime Minister Yingluck Shinawatra said officials have identified the group behind the Saturday attacks, but would not say who it was because of the ongoing investigation.
"We have clues who the bombers are, but details could not be released as (I) want (the police investigative team) to work on this comfortably," she said, according to MCOT.
Security in the region has been beefed up.
The Muslim-dominated southern provinces in the majority-Buddhist country has seen frequent flareups in violence.
Insurgent groups there have complained that the government has not justly represented them.