Bangkok (AFP) - Thai police on Monday accused a network of "Red Shirt" supporters of the toppled government of trying to destablise the kingdom after the second small bomb attack to hit Bangkok in recent weeks.
Two men were detained on Saturday night after a brief shoot-out with security forces that followed a grenade attack at the Criminal Court, which caused minor damage to the building's car park but no injuries.
National Police spokesman Prawut Thavornsiri said they are hunting another man and two women from the same apparent cell.
"Based on our investigation they have links with the Red Shirts," he told AFP.
His boss, Police General Somyot Poompanmoung, said the blast was carried out by the "same network of people" responsible for twin pipe bombs that exploded last month outside a downtown shopping mall, slightly injuring two people.
That incident was the first major disruption to an uneasy peace imposed under martial law since last May's coup that removed the elected government of Yingluck Shinawatra.
"I think there are many groups attempting to do a similar thing," Somyot told reporters, vowing to arrest anyone linked to the group.
The Red Shirts is a grassroots political movement that opposes the coup and supports the fallen government of Yingluck -- whose family have dominated Thai politics for more than a decade.
But their resistance to the coup has been muted, with Red Shirt leaders under observation by the military and warned against breaching martial law by organising political rallies.
Red Shirt leader Jatuporn Prompan dismissed the link with his group, insisting they were non-violent and have nothing to gain from stoking tensions under martial law.
"We are not involved. It would be a disadvantage to us... no-one is that stupid," he said on his daily television programme.
Pressure has been mounting on the junta to lift martial law, with an increasing number of political figures and campaigners grumbling that debate is being stifled just as Thailand needs it most.
The junta-picked National Legislative Assembly is next month due to deliberate on a draft constitution, which the junta says will provide the bedrock for a return to democracy.
But critics doubt whether a new charter will bridge Thailand's deep political divisions.
Junta chief and Prime Minister, Prayut Chan-O-Cha, who has so far resisted calls to end martial law, said the bombers wanted to revive tensions but declined to directly link them to the Red Shirts.
"The perpetrators want to create panic and chaos... in order to make the public aware that they still exist," he told reporters.
Thailand has been blighted by nearly a decade of political turmoil since billionaire former premier Thaksin Shinawatra -- Yingluck's brother -- shook up the establishment by winning elections with his populist politics.
Parties led by Thaksin, his family or affiliates have won every election since 2001, in the process facing two coups and the disposal of three premiers by Thailand's interventionist courts.