Police hunting those responsible for Thailand's deadliest bombing arrested a second foreign suspect on Tuesday, Prime Minister Prayuth Chan-ocha said.

The Aug. 17 attack on a Bangkok Hindu shrine killed 20 people and injured more than 100. Fourteen foreigners were among those killed in a blast the military government said was aimed at dealing a blow to an already ailing economy.

The man was arrested in Sa Kaeo province, on the border with Cambodia east of Bangkok. The suspect was being transferred to Bangkok for questioning.

"We have arrested one more, he is not a Thai," Prayuth told reporters after a weekly cabinet meeting. He did not elaborate.

Television footage of the suspect showed a thin man in a baseball cap, sunglasses and with a short mustache.

Also read: Suspected bomb blast injures nine at Bangkok bus stop

The arrest came after security forces detained a first foreign suspect in weekend raids on the outskirts of Bangkok, in which they also found explosives.

Police said they had transferred 22 officers from their posts for negligence. The transfers came just a day after the police chief promised a reward to investigators for making the first arrest.

Six of the 22 were immigration officers from Sa Kaeo, while the others worked in the Bangkok districts where the security forces conducted the weekend raids.

Thai police chief Somyot Pumpanmuang said he transferred the immigration officers because foreigners had been able to enter Thailand illegally in Sa Kaeo.

"That was my decision," he said. "I think that when a foreigner is able to illegally enter Thailand without proper scrutiny... I think those officers should be transferred."

Police have been criticized for an erratic investigation, which had made little progress until the weekend. Police issued arrest warrants for a Thai woman and a foreign man on Monday.

Read more: Foreigner arrested in Bangkok bombing

The woman, Wanna Suansuant, has contacted authorities and would meet police, Somyot said on Tuesday. He gave no details.

Her family told police on Monday she traveled to Turkey to work with her partner and child two to three months ago.

Police have been looking into a possible Turkish connection. Fake Turkish passports were seized and police requested a Turkish translator to assist in questioning the 28-year-old man they arrested on Saturday.

The authorities have not confirmed his identity or nationality. He is charged with possessing illegal explosives.

Speculation has centered on sympathizers of Uighur Muslims, opponents of the government, southern ethnic Malay rebels and foreign extremists, among other groups.

Thailand drew international outrage in July when it forcibly repatriated more than 100 Uighurs to China.