Police in Bangkok say they have arrested one of the suspects in the bombing that killed 20 people earlier this month.

The man, who has been named as Adem Karadag, was arrested after police raided an apartment in the city's north.

They found a fake Turkish passport, many other passports and suspected bomb-making materials, including explosives and a detonator.

They would not confirm his nationality.

The man seen in the video was believed to have carried out the bombing, which police said they believed was planned by a network.

But in a news conference later on Saturday they instead said that the suspect they had arrested was not the bomber seen in the video.

"We believe he is a culprit in the same network. More details will be given later," a police spokesman said.

Police chief Somyot Poompanmoung also said the bomb materials found were "the same, similar or the same type" as the ones used in the two bombs.

Asked what could be the motive for the bombing, Somyot said "it's a personal grudge .. not international terrorism." He did not explain what he meant.

The blast happened at 7pm (1pm Irish time) near the Erawan Hindu shrine in the downtown Chidlom district - a shopping hub popular among tourists.

Many of those killed were tourists and at least 117 people were wounded, some of whom lost limbs.

CCTV footage showed a huge orange fireball as the bomb exploded and people fleeing down the street.

Police were facing growing public pressure to catch the perpetrator, but last Monday they had admitted in a news conference that the trail had gone cold.

It is thought the attacker first took a motorcycle away from the shrine before travelling in the taxi from Bangkok's central business district to the city's main train station.

However, 75% of the security cameras along the attacker's getaway route were broken at the time.

The investigation was also hampered by a lack of sophisticated equipment, with a national police chief saying: "Have you seen CSI? We don't have those things."