Thai police have said they are hunting for more suspects after arresting a "foreign" national over the recent Bangkok bomb blast. The nationality of the 28-year-old man, who possessed several fake passports at the time of his arrest, is still unclear.

Investigators say the arrested man, whose nationality and identity have not been revealed, was part of the shrine attack but ruled out he was the primary suspect. A large cache of bomb-making materials was seized from his residence when they arrested him at Poon Anand Apartments in Nong Chok District.

The explosion on 17 August in Erawan Shrine killed 20 people, including 14 foreigners, sending shockwaves across Thailand. The police have come under intense pressure for not doing enough in catching the perpetrators. No group has claimed responsibility for the explosion. A backpacker who was seen leaving his bag at the shrine turned out to be a key suspect. He remains at large.

"We've seen two of them, frequently. One was the arrested man, but there's another, he's much taller," one of the residents in the same apartment complex, where the suspect was arrested, told Reuters on condition of anonymity.

Law enforcement officials have refused to reveal whether they have received any vital information from the detained man. However, sources have told the Bangkok Post that the suspect is thought to have delivered the explosives to the bomber, who was seen wearing a yellow T-shirt at Hua Lamphong train station. The bombers are feared to have fled the country.

The suspect was taken into military custody at an undisclosed location following his brief interrogation at a local police station. The police were visibly furious when questioned whether the suspected was being made a scapegoat owing to the pressure on officials. "How can you ask such a question? Are you Thai? It's completely unhelpful," national police chief Somyot Poompanmuang responded.

Speculation has been rife over the involvement of various groups including ethnic Malay insurgents and Uighur extremists in the bombing. However, authorities have not confirmed any of such claims as yet.