Thailand's Prime Minister Surayud Chulanont has met security chiefs after a wave of bombings and shootings that killed at least seven people.
One of the bombs killed an army major
Some 30 bombs went off in southern Thailand in one of the region's worst outbreaks of violence since a Muslim insurgency flared up three years ago.
Schools, bars, hotels, a car showroom and a power station were targeted.
Thai officials believe the attacks were timed to coincide with the start of the Chinese New Year celebrations.
Speaking after the prime minister's emergency talks with military and security chiefs, Thailand's army chief-of-staff warned that there could be further attacks.
"The violence may increase, and it will be the same kind of terrorist tactics," General Montri Sangkasap said.
He said the authorities were still unsure about who had carried out the attacks.
And he warned that, since they had happened as Thailand's many ethnic Chinese were celebrating Lunar New Year, extra vigilance would be needed around the time of other festivals.
Three people died on New Year's Eve on 31 December when a series of bombs exploded in the capital Bangkok.
Home to most of Thailand's 4% Muslim minority
Muslim rebels fought the government up to the mid-1980s
Suspected militants have upped attacks since 2004, targeting Buddhists
Security forces' response criticised by rights groups
Gen Montri said security forces would now be placed on extra high alert during the Makhabucha festival on 5 March and the Songkran Thai New Year celebrations in mid-April.
Army spokesman Col Acra Pritroch said the aim of the attackers was to show that the government could not maintain security during the Lunar New Year.
"They use the festival time to show that there is not peace in the three provinces in the south," he said on Thai television.
The most recent blasts happened about 1900 (1200 GMT) on Sunday.
Petrol stations, karaoke bars, hotels, a golf course and a cinema were hit in the southern province of Yala.
At least one person was killed in blasts at five karaoke bars in Narathiwat province. Two public schools in the province also were torched.
Firebombings targeted electricity transmitters in Pattani province, causing power blackouts across Pattani town, police said.
Three people were shot dead by unidentified assailants. An army major was killed, and his seven-year-old son wounded, by a bomb left in a bag outside his home.
At least 45 people were injured in the wave of attacks.
Police have advised people in the southern provinces to stay at home following the attacks.
Nearly 2,000 people have been killed in Thailand's south since an insurgency was launched there in January 2004.
Violence has surged since the military seized power in a bloodless coup in September.
On Friday, Gen Surayud said Thailand was willing to hold talks with separatists with the help of neighbouring Malaysia in the army-appointed leader's latest olive branch.
Most of the population in the region are ethnic Malays who have long felt discriminated against by the Buddhist majority in Thailand, the BBC's Jonathan Head in Bangkok says.