BANGKOK — Thai police said Saturday that they are looking for a 10th suspect in last month’s bombing of a landmark in central Bangkok that killed 20 people.

Authorities will seek an arrest warrant soon for a man who shared an apartment with a suspect who was arrested a week ago when a police raid found bomb-making materials in his room, said national police spokesman Lt. Gen. Prawut Thavornsiri, adding that the man’s nationality was unknown.

The arrested man, who is facing a main charge of illegally possessing explosives, was brought to court Saturday to obtain permission for his detention to be extended. When he was arrested, police found a fake Turkish passport in his apartment carrying the name Adam Karadag, but now call him Adem Karadak.

Another man was arrested near the border with Cambodia. Neither of the arrested men’s nationalities has been confirmed.

Arrest warrants have been issued for seven other suspects in the Aug. 17 attack at Bangkok’s popular Erawan Shrine, which also injured more than 120 people. Thai authorities say that at least two of the suspects are believed to be Turkish.

Prawut said that a sketch of the new suspect had been completed, but that police were waiting on seeking a warrant until a witness could confirm its likeness. He suggested that the suspect was deeply involved in the gang that is believed to have carried out the bombing at the shrine, and another one the next day near a busy Bangkok river pier that caused no casualties when the bomb exploded in the water.

“There is nothing else to update because it’s still on secret operations,” Prawut said. “But it’s getting close now that we will be able to reveal. We expect some developments next week.”

Police seemed to have progressed quickly in their investigation since the first raid on an apartment in Bangkok’s outskirts on Aug. 29.

There had been speculation that the foreigner arrested at the border near Cambodia was the yellow-shirted man seen in security videos apparently planting the deadly bomb near the shrine. The bomber is believed to have left a pipe bomb in a knapsack at the open-air shrine when it was packed with worshippers during evening rush hour.

However, Prawut said Friday that DNA samples taken from the suspect did not match the DNA found on evidence that the bomber is believed to have left behind – in a taxi, on banknotes and on a motorcycle taxi he took the night of the attack.