A Thai military court issued an arrest warrant on Tuesday for a second suspect in connection with a wave of deadly bomb attacks last week that killed four people and injured dozens, police said.
Explosions rocked seven provinces in Thailand's south on Thursday and Friday, just days after Thais voted to accept a military-backed constitution.
No group has claimed responsibility but police and senior officials have publicly ruled out any link to foreign militants.
"The court has approved the arrest warrant for one suspect for the explosions. We can't say who that individual is," said Chaiyapol Chatchaidet, commander of the Counter Crime Planning Division.
It was the second arrest warrant issued in connection with the wave of attacks. Police on Sunday said they had arrested one suspect for arson.
Defence Minister Prawit Wongsuwan on Monday said the attacks might have involved southern insurgents hired to carry out the bombings but said the bombings were not an extension of a bloody separatist war in the country's three southern-most Muslim-dominated provinces.
Security experts told Reuters official denial of involvement by Malay-Muslim insurgents was unsurprising as admitting that southern insurgents could be involved would have serious economic and security implications for Thailand.
Thailand is a mainly Buddhist country, but the three southern provinces of Pattani, Yala and Narathiwat are majority-Muslim and resistance to central government rule has existed there for decades, resurfacing violently in 2004.
More than 6,500 people have been killed in the region since 2004 in bombings, shootings and arson attacks according to Deep South Watch, a Pattani-based group which monitors the conflict.