Five arrest warrants have been issued in connection with Saturday's grenade attack on Bangkok's criminal court, as security was tightened around the capital.
Four suspects are in custody, including two men arrested immediately after the incident.
Prime Minister Prayut Chan-o-cha, meanwhile, asked the people to be on alert, after a suspect detained following the blast claimed that it was part of a larger plot to create unrest throughout the country.
"I will not bow to bad people," the Premier said yesterday.
No one was hurt in the attack, which took place barely one month after two pipe bombs exploded on a busy walkway linking a train station and a popular shopping mall in downtown Bangkok.
The culprits for that explosion have yet to be arrested.
On Saturday night, however, military officials say plainclothes officers who were trailing two men on their motorbike arrested them shortly after one of them hurled a grenade into the carpark of the courthouse.
Arrest warrants were issued for the duo and at least three other suspects. Four people are now in military custody.
Under martial law, which has been in place nationwide since May 20 last year, the military can detain a person without charge for up to seven days.
One of the suspects in the grenade attack, Mahahin Khunthong, claimed that he had been offered 10,000 baht (S$423) to carry out the attack, and that there were plans for more attacks nationwide to sow unrest.
National police chief Somyot Pumpanmuang told reporters yesterday that the people behind both attacks are from the same network.
Investigators are also checking possible links between the attacks and the "red shirts", a political movement that supported the Puea Thai-party run government deposed by the military last May.
Puea Thai is backed by Thaksin Shinawatra, who was prime minister until he was toppled by a military coup in 2006 and now lives abroad to evade a jail sentence.
The military government has steadily dismantled his influence in the administration and suppressed the red shirts since coming into power.
At a press conference on Sunday, it was also revealed that Mahahin was acquainted with Thaksin's cousin, former army chief Chaisith Shinawatra.
General Chaisith met reporters yesterday, saying that the suspect had asked him for help previously.
But he denied having anything to do with the attack.
"Do not fabricate (details), don't drag me in," he was quoted by local media as saying.
"In any case, I am not running away."
Meanwhile, a new Constitution being drafted by a hand-picked committee has drawn criticism for reducing the role of direct elections.
It has drawn flak from even the Democrat Party, which actively supported the campaign to oust the Puea Thai government before the coup.
Gen Prayuth, who has promised to hold a general election by next year, has frequently warned that martial law cannot be lifted and elections held if there is continued opposition to junta rule.
This article was first published on March 10, 2015.
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