BANGKOK (AP) -- Thai police issued arrest warrants Monday for two more suspects, a Thai woman and a foreign man of unknown nationality, and released their images in the widening investigation into Bangkok's deadly bombing two weeks ago that yielded its first arrest over the weekend.
National police spokesman Prawuth Thavornsiri said he was certain the two were part of a group police say was responsible for the Aug. 17 blast at the Erawan Shrine in central Bangkok that killed 20 people, more than half of them foreigners.
During a televised statement on Monday, Prawuth displayed a photograph of the woman's Thai identification card showing a young woman in a black headscarf and a sketch of the man. He later said police were asking for additional arrest warrants.
Thailand's national police spokesman Prawut Thavornsiri holds a tablet displaying a picture of an unnamed foreign man, wanted for questioning after bomb making materials were found in a Bangkok apartment he allegedly rented, at the police headquarters in central Bangkok on August 31, 2015. Thai police 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. (NICOLAS ASFOURI/AFP/Getty Images)
Thailand's national police spokesman Prawut Thavornsiri holds a tablet displaying a picture of Wanna Suansan, 26, wanted for questioning after bomb making materials were found in a Bangkok apartment she allegedly rented, at the police headquarters in central Bangkok on August 31, 2015. (NICOLAS ASFOURI/AFP/Getty Images)
The development came after police arrested a man from an apartment in Bangkok's outskirts on Saturday and seized bomb-making equipment that included detonators, ball bearings and a metal pipe believed to be a bomb casing.
Thai police, meanwhile, awarded themselves a 3 million baht, or $84,000, reward Monday for tips leading to the arrest of bombing suspects.
National police chief Somyot Poompanmoung said he was taking the unusual step of giving the reward to the police force both to motivate his officers and to show that Thailand's police are good at their job.
"This money should be given to officials who did their job," he said at a news conference as aides brought out stacks of 1,000 baht notes. It wasn't immediately clear how the money would be distributed to police officers.
More bomb-making materials were discovered in a second apartment during a raid Sunday in a nearby neighborhood, said Prawuth. He said the second apartment, in a neighborhood known as Min Buri, was rented by the Thai woman identified as 26-year-old Wanna Suansun. He said the woman has a house registration in the southern Thai province of Phang Nga, and is also known by the name Mai Saloh.
Prawuth described what police found in the second apartment as "important bomb-making materials such as gunpowder, urea-based fertilizer which can be used as explosive powder when mixed with other substances, a remote-controlled car with its controller which can be used as a detonator, nuts and bolts, small light bulbs and digital watches," among other things.
The arrest warrants for them say they are wanted on a charge of conspiracy to possess unauthorized war material, a reference to the gunpowder.
The wanted man, whose face is shown in a police sketch with short brown hair and a light beard and mustache, is believed to have lived in the apartment, said Prawuth, adding that his nationality was not known. He told The Associated Press the man's name is Jusuf, but did not explain how he learned that or give a precise spelling.
No one has claimed responsibility for the attack, sparking an array of theories about who might be behind it. Police have suggested that the suspects were part of a people-smuggling group who held a grudge against Thai authorities.
Much remains unknown about the man arrested Saturday, including his nationality and his motive. On Sunday, Prawuth said police were working with "a number of embassies" and interpreters to try to establish the man's nationality, adding that he did not speak Thai but spoke some English.
Speculation has grown that the suspect might be part of a group seeking to avenge Thailand's forced repatriation of ethnic Uighurs to China after images circulated online of a fake Turkish passport found in his apartment bearing his apparent picture.
Uighurs are related to Turks, and Turkey is home to a large Uighur community.
Authorities have dodged questions about whether the suspect is believed to be Turkish, saying that he was traveling on a fake passport.
The Turkish Embassy in Bangkok could not immediately be reached for comment. A Turkish government spokesman contacted over the weekend in Istanbul said he had no information on the suspect or any possible Turkish link to the attack.
Another possibility is that the perpetrators are Muslim separatists from southern Thailand, opponents of Thailand's military government and feuding factions within the security services.
The blast at the Erawan Shrine was unprecedented in the Thai capital, where smaller bombs have been employed in domestic political violence over the past decade, but not in an effort to cause large-scale casualties.