Thailand's prime minister said a foreign man believed to be a "main suspect" in the Bangkok bombing was arrested Tuesday at a checkpoint on the Cambodian border, the second foreigner to be detained.
The August 17 blast tore through a religious shrine in central Bangkok and killed 20 people, mostly ethnic Chinese tourists.
Prayut Chan-O-Cha, who also heads the nation's junta, was asked by reporters to comment on rumours another person had been detained.
"It's true. He has been arrested at Sa Kaeo checkpoint," Prayut said, referring to the Thai side of a border crossing with Cambodia.
Asked whether he is thought to be the person who planted the bomb at the Erawan shrine in Bangkok's busy Chidlom shopping district, he replied: "We are interrogating. He is a main suspect and a foreigner."
The "important" suspect was arrested "this early morning" he said, adding he was "probably running away".
The checkpoint is located at a bustling and seedy border town which is a transit route for smuggled goods between the two countries.
The motive for the shrine attack -- Thailand's worst single mass-casualty attack -- remains shrouded in mystery.
Suspicion has alternated between Thailand's bitter political rivals, organised criminal gangs, Islamist militants, rebels in the kingdom's strife-torn south and sympathisers of refugees from China's Uighur minority.
In July Thailand deported 109 Uighurs to China, enraging supporters of the minority who allege they face torture and repression back home.
Turkish protesters stormed the Thai consulate in Istanbul and forced it to close.
The shrine is popular with ethnic Chinese visitors to Bangkok.
The hunt for the perpetrators of the bomb blast has been characterised by confusing and at times contradictory statements from police and junta officials.
But the tempo of the investigation has increased since the weekend when the first arrest was made.
The foreigner was detained on Saturday at a flat in a Bangkok suburb, allegedly in possession of bomb-making paraphernalia and dozens of fake Turkish passports.
He is in military custody but has not been publicly identified.
Police have speculated that the attack was in retaliation for a crackdown on a major people-smuggling network.
But analysts say crime alone was unlikely to be the motivating factor behind a bomb that brought such carnage.
A junta spokeswoman said in a broadcast the ongoing interrogation of the foreigner detained Saturday had led to "the apprehension of additional suspects".
The broadcast was made before the announcement by Prayut.
Arrest warrants have been issued for several people including three unnamed males.
The only named warrant is for a 26-year-old Thai Muslim woman called Wanna Suansan. Police say she rented a separate flat also in the city suburbs where bomb-making equipment was also found.
They issued a sketch on Monday of an unknown male suspect believed to have rented the flat.
Thai authorities confirmed Tuesday that Wanna is overseas but refused to say in which country.
Late Monday AFP tracked down her number and a woman answering that name took the phone call, saying she was living in the Turkish city of Kayseri with her husband whose nationality she did not state.
The number was for a Turkish mobile phone.
In her phone interview Wanna denied involvement in the blast, saying she had not visited the flat where the bomb-making equipment was found for around a year.
Instead, she said it had been rented to a friend of her husband.
National police spokesman Prawut Thavornsiri told reporters Tuesday that officers had searched her parents' home in the southern province of Phang Nga.
"Her parents said she was not there, she was abroad. We are coordinating for her to come talk to police," he said, without revealing her presumed whereabouts.