Thai police on Monday said they had found bomb-making materials over the weekend in a second apartment following the arrest of a suspect over the Bangkok shrine bombing that left 20 people dead.

Thai police on Monday said they had found bomb-making materials over the weekend in a second apartment following the arrest of a suspect over the Bangkok shrine bombing that left 20 people dead.

"We found fertilizer bags, watches, radio controls -- parts to make bombs and electric charges," national police spokesman Prawut Thavornsiri told AFP on Monday.

He said the items were found during a raid on an apartment in the northeastern suburb of Minburi over the weekend. He did not detail when the raid took place.

Media accompanied police during a search of multiple flats in Minburi on Sunday but no items were shown to the press or announcement made of any evidence discovery.

The area is near to where an unidentified foreigner was arrested on Saturday, allegedly in possession of bomb-making paraphernalia including detonators and ball-bearings as well as dozens of fake passports.

Police believe the suspect was part of a crime group who helped illegal migrants obtain counterfeit documents -- and that the bomb attack on the shrine was retaliation for a recent crackdown by Thai authorities.

The blast that hit the Erawan shrine in a busy Bangkok shopping district on August 17 was Thailand's worst single mass-casualty attack, killing 20 people -- most of them ethnic Chinese tourists from across Asia.

Thai authorities have played down any suggestion the attack was launched by international terrorists or specifically targeted Chinese tourists.