A second foreign suspect has been arrested in connection with the deadly bombing at a Bangkok shrine in August, the Thai prime minister has said.
The male suspect was arrested in Sa Kaeo province, east of Bangkok on the border with Cambodia, Prayuth Chan-ocha told reporters.
He described the man as "a main suspect".
A foreign man was arrested in Bangkok on Saturday over the blast at Erawan shrine, which killed 20 people.
Thai military authorities have been interrogating the 28-year-old man, but they have not yet released his name or nationality.
Bomb-making materials and forged passports were found at the apartment where he was detained in Nong Jok on the outskirts of Bangkok, and he has been charged with possessing illegal explosives, police said.
It is unclear whether either of the two arrested men is the suspect seen on a security camera leaving a backpack at the crowded shrine shortly before the bombing on 17 August.
Thai authorities have issued three more arrest warrants - making seven in total.
The Thai investigation into the bombing is gaining momentum, says the BBC's Jonathan Head in Bangkok.
The latest developments in this case suggest police are dealing with a militant network - a network that could have been planning more attacks, he says.
But the motive for the bombing - unprecedented in its scale in Thai history - is still unknown, although several analysts have suggested it may be linked to the deportation of Muslim Uighurs from Thailand to China.
'The key suspect'
"We have arrested one more, he is not a Thai," Mr Prayuth told journalists after his weekly cabinet meeting, calling him "a main suspect and a foreigner".
Images of the detainee in military custody showed a tall, thin man with trimmed facial hair, wearing sunglasses and a baseball cap.
At a news conference, Thailand's national police spokesman Lt Gen Prawut Thavornsiri said the man was intercepted as he attempted to cross the border illegally into Cambodia.
Thai media circulated a photo of a Chinese passport which was claimed to belong to the man detained on the border. On the passport, he is identified as Yusufu Mieraili, 25, from Xinjiang province - home to a significant Muslim Uighur population.
One police investigator also identified him as "Yusufu", Thai media said.
Thailand controversially repatriated more than 100 Uighur Muslims to China in July.
View from China - John Sudworth, BBC News, Beijing
China will be watching the investigation in Bangkok closely.
Speculation about who was behind the bombing has ranged widely, but has included the suggestion that it was carried out by sympathisers of China's predominantly Muslim, Uighur minority.
China has long faced criticism for the perceived harsh restrictions it places on religion and culture in its western Xinjiang region - where the majority of Uighurs live - and Thailand recently found itself in the spotlight following its forced repatriation of more than 100 Uighurs to China.
If it is confirmed that the suspect was found in possession of a Chinese passport, it will throw the spotlight on an ethnic conflict that China has long argued poses an international threat.
Attacks allegedly carried out by Xinjiang-based groups against Chinese targets have intensified in recent years, including a suicide attack in Beijing's Tiananmen Square and a knife attack at Kunming Station that left more than 30 people dead.
But although some Uighur militants have reportedly been involved in foreign conflicts, there has been little evidence to show any more sophisticated cross-border links.
Thai authorities have also released details of the three new suspects for whom they have issued arrest warrants. One suspect is an unidentified Turkish man, another a foreign man named Ahmet Bozoglan and a third a foreign man named Ali Jolan.
All face charges of illegally possessing explosives.
On Monday, Thai police issued arrest warrants for two suspects - a 26-year-old Thai Muslim woman, Wanna Suansan, and an unnamed foreign man.
However, a woman who claims to be Ms Suansan told AFP news agency from Turkey that she had last been in Thailand three months ago.
She said she was "shocked" to have been named as a suspect.
Also on Tuesday, police said they had transferred 16 officers - including senior officers - from their posts in Bangkok districts for negligence.
An additional six immigration officers were transferred from their posts in Sa Kaeo, where Tuesday's arrest took place, reported Reuters news agency.
Police chief Somyot Pumpanmuang was quoted as saying the immigration officers had been transferred because it had emerged that foreigners had been able to enter the country illegally.
The transfers came just a day after the same police chief said he would reward his own men for making the first arrest.