Thai Prime Minister Thaksin Shinawatra has vowed tough action against the killers of two marines in the nation's troubled south on Wednesday.
The marines were taken hostage and then killed by villagers
Mr Thaksin blamed Muslim insurgents for killing the men, who were taken hostage in Tanyong Limo, Narathiwat province.
Relatives of the dead men held a funeral service for them on Thursday.
Princess Sirindhorn represented the royal family at the service, in an indication of how seriously Bangkok is viewing this latest incident.
Thailand's largely Muslim southern provinces have been hit by a wave of violence since early 2004, leaving more than 900 people dead.
The government has blamed Muslim separatists, while local people have been angered by the security forces' often brutal suppression of the violence.
In response to Wednesday's incident, Malaysia has ordered security on the border with Thailand to be stepped up.
Defence minister Najib Tun Razak told local media that the aim was to stop Thai militants from launching attacks from Malaysian territory.
"The cruelty that the killers have done to fellow human beings is beyond my imagination," Captain Traikwan Krairiksh, the commander of the two marines, said at the funeral.
SEQUENCE OF EVENTS
At least one person is killed and three injured in a shooting incident on Tuesday evening
Two marines kidnapped by local mob soon afterwards
Hostages taken to local school
Villagers set up roadblocks on Wednesday, preventing troops from entering
Hostages killed, reportedly as villagers heard rumour of a possible attack
Laddawan Thongeiat - wife of Petty Officer Khamthon Thongeiat - criticised the authorities for her husband's death.
"The government knew what was going on and they knew that the militants were holding them but they couldn't help," she told Reuters news agency.
Mr Thaksin pledged on Thursday that while "there is not going to be retaliation... there will have to be law enforcement".
The government's hard-line policy in the south has often been criticised as too harsh - and analysts feared that the killing of the two marines could lead to a fresh clampdown in the area.
The atmosphere in Tanyong Limo was reported to be muted on Thursday. Many men have left the area.
Instead, teams of security personnel have been combing the village for clues to the identity of the killers.
Home to most of Thailand's 4% Muslim minority
Muslim rebels fought the government up to the mid-80s
Suspected militants have upped attacks since 2004, targeting Buddhists
Security forces' response criticised by rights groups
Thailand's leading pathologist Porntip Rojanasunun told reporters there was enough evidence to arrest the perpetrators.
"Authorities have clear evidence that three men in the village cruelly killed the hostages," Defence Minister Thammarak Isarangura added.
The incident began when the two marines were taken from their car on Tuesday night, after villagers accused them of firing shots in connection with an attack on a local teashop.
Thai officials insisted the men were investigating the shooting, rather than being involved in it.
After taking the two men hostage, villagers then prevented security forces from entering the area.
Amid fears that troops would attack, the two marines were bludgeoned and stabbed to death.