BANGKOK (AFP) - Thai police on Friday (Sept 4) said neither of the two men detained over the deadly Bangkok attack last month were believed to be the main bombing suspect - seen on CCTV wearing a yellow T-shirt and placing a rucksack under a bench at the Erawan Shrine moments before the blast.

The two foreign suspects - identified as Adem Karadag and Yusufu Mieraili but whose nationalities remain unconfirmed - are thought to be part of a group behind the Aug 17 blast at the religious shrine that killed 20 people.

The arrests have been seen as a potential breakthrough in the investigation but on Friday, the police said evidence has suggested neither are the main suspect.

"Evidence has showed that Yusufu was probably not the yellow-shirt" suspect, national police spokesman Prawut Thavornsiri told reporters at a press conference in Bangkok.

He added that "nothing had confirmed" Karadag was the chief suspect, referring to DNA tests without elaborating on the exact checks conducted.

After nearly two weeks without progress on the unprecedented bombing, the authorities on Saturday arrested Karadag in a raid on a flat on the eastern outskirts of Bangkok, their first blast-related arrest.

Mieraili was detained three days later while trying to cross into Cambodia, according to Thai police.

Both men have now been charged with possessing "illegal bomb weapons", Prawut said on Friday, after Karadag was allegedly found in possession of bomb-making paraphernalia and Mieraili's DNA was matched with that in another raided flat where the police found bomb-making materials.

The authorities have refused to confirm the two arrested men's nationalities as they believe both used fake identity documents and are still liaising with embassies.

Karadag was found with dozens of fake Turkish passports while Mieraili carried a Chinese passport.

A further seven people are wanted over the crime including a Turkish national named as Emrah Davutoglu by police on Wednesday, the first time Thai authorities have revealed the nationality of a foreign suspect of the attack.