An image released by the Royal Thai Police on August 19, 2015, shows a sketch of the main suspect in Monday's deadly blast, in central Bangkok, Thailand, Aug 19, 2015.[Photo/Agencies]

BANGKOK - Police probing Thailand's deadliest bombing widened their net in the search for more suspects on Sunday after a foreigner was arrested and stacks of fake passports and bomb-making materials were found during a raid on a Bangkok apartment block.

The 28-year-old man, who has been in Thailand since January 2014, was detained on charges of possessing illegal explosives. Police have not revealed his identity or nationality.

The Aug 17 bomb at Bangkok's Erawan Shrine, where Thais and Asian tourists flock each day, stunned Thailand.

Fourteen foreigners, seven from China, were among the 20 killed in an attack the ruling junta said was intended to cripple an already flagging economy.

Police have been criticised for an erratic investigation that had, until this weekend, uncovered few clues about who was behind the blast. No group has claimed responsibility.

Officials declined to say if the man arrested had provided new information, but deputy national police chief Chaktip Chaijinda told Thai television more suspects were being sought.

Suspect not alone

Police and residents in Bangkok's Nong Chok district said the suspect rented four apartments on the same floor of the rundown building.

A man and woman living on the same floor said the suspect did not live alone and they had seen a taller man with similar appearance entering and leaving several times each day. They had not seen the second man since Friday.