Police said on Tuesday they had arrested two alleged members of separatist groups active in the southern provinces of Yala, Pattani and Narathiwat, which were part of an independent Malay Muslim sultanate until they were annexed by predominantly Buddhist Thailand in 1909.
At least 5,000 people have died in the region since violence flared up again in 2004 after a hiatus.
"The intelligence we have gathered shows unrest is likely to increase during April and May," Yuthasak Sasiprapa, a deputy prime minister and retired general, told reporters.
He said he had met army chief Prayuth Chan-ocha. "We concluded we will not negotiate with the attackers."
However, Sukampol Suwannathat, Thailand's defense minister and a former air force officer who is due to visit the area on Friday, declined to rule out talks.
The present government and its predecessor are thought to have held talks with separatist figures but there has been no official confirmation.
On Saturday, two bombs hidden in pick-up trucks exploded in a busy shopping street in Yala, killing 10 people.
A third blast 140 km (87 miles) away in Hat Yai, a regional trade and tourism hub, in the basement car park of a five-star hotel and shopping complex killed three more people, including a Malaysian traveler. In all, the attacks wounded more than 300 people.
"Innocent people were killed. The attackers did not discriminate between Buddhists and Muslims," Prayuth told reporters, adding: "If further attacks take place then martial law will be declared in Hat Yai."
The three southern provinces are already covered by a tough emergency decree that gives the military wide-ranging powers of search and arrest.
Hat Yai is the biggest city in the neighboring province of Songkhla, which is not covered by the decree. Four Songkhla districts are covered by a less drastic security law but Hat Yai is not included.
Prime Minister Yingluck Shinawatra flew to Hat Yai on Monday to visit the injured.
The scale of the bombings on Saturday and the fact that large numbers of civilians were targeted in a tourist area has worried some analysts although the insurgents' aim is unclear.
Hat Yai has been targeted by several powerful bombings since 2005, all blamed on militants, but most attacks in the South have been limited to the three southernmost provinces and have not touched nearby tourist areas like Phuket or Krabi.
After the latest attacks, concerns were raised over safety in Hat Yai, which is a popular destination for Malaysian tourists during Thailand's Songkran water festival, which starts next week.
(Reporting by Pracha Hariraksapitak and Amy Sawitta Lefevre; Editing by Alan Raybould)
Reuters
