At least two people have been killed and several injured after a bomb exploded in southern Thailand.
Tensions are high in mainly-Muslim southern Thailand
The blast happened at a Siam Commercial Bank branch in Sungai Kolok, a town in Narathiwat province, police said.
More than 550 people have died this year in a wave of attacks and clashes between militants and officials.
In one of the most serious incidents, 85 Muslim protesters died in the town of Takbai in October. Many of them suffocated to death in police custody.
Prime Minister Thaksin Shinawatra said on Friday that three army commanders would be investigated in connection with these deaths.
At least five people were wounded in the bomb in Sungai Kolok, which police said was planted in a motorcycle parked in front of a cash machine beside the bank.
The incident was the third major blast in the town since March, when a bomb wounded 28 people.
Home to most of Thailand's 4% Muslim minority
Muslim rebels fought the government up to the mid-80s
Suspected militants have upped attacks this year, targeting Buddhists
Security forces' response criticised by rights groups
In October another bomb at a nightlife area in the town killed a
Malaysian tourist and a bar worker, and wounded 20 others.
Correspondents say border security in this area is very lax, and many locals pass through unchecked.
Thailand has claimed that separatist guerrillas may be crossing from Malaysia, a charge the Malaysian authorities deny.
Friday's blast came after a top security official warned of the danger of an upsurge in attacks next year, and police said they were ordering an extra 2,000 officers to reinforce security in the southernmost provinces.
Thousands of teachers in the south went on indefinite strike on Thursday, urging the authorities to do more to protect them from attacks by Muslim militants.
Teachers are perceived by the rebels to be representatives of the Buddhist-dominated administration.
Tensions in southern Thailand rose dramatically after 85 Muslim protesters were killed in October in the southern town of Takbai, when the army tried to stop their demonstration.
Seven were shot and 78 were suffocated or crushed to death when they were loaded into army trucks.
A government-backed inquiry into the incident found that the deaths were not deliberate.
But Prime Minister Thaksin Shinawatra admitted the panel found that some senior officials had failed to do their jobs, and left it to subordinates to handle the protest's outcome.
On Friday he named three people who would be investigated further to determine whether they were to blame for the deaths in any way.
A panel would look at why General Pisarn Wattanawongkhiri, his deputy, and another senior officer did not personally supervise the
transportation of the protesters during their long truck journey to an army base, Mr Thaksin said.