Thai police on Wednesday issued an arrest warrant for an individual they described as a "foreign man", in connection with a bomb blast in Bangkok that killed 20 people, including several foreigners.
A court approved the arrest warrant, Thai police spokesman Prawut Thawornsiri said.
The warrant says police are seeking “a foreign man, unnamed, according to the sketch”, referring to a sketch released earlier in the day that showed a fair-skinned man with thick, medium-length black hair, a wispy beard and black glasses.
The man could be of “mixed origin”, Mr Prawut said in a televised interview.
Police also said two other men seen in grainy CCTV footage near the scene of the blast are suspects, bringing to three the number of individuals they are seeking.
“The person in red and the person in white are also suspects,” the spokesman said.
Police earlier on Wednesday said they had not yet established the nationality or whereabouts of the main suspect, suggesting the trail had gone cold after he was captured on CCTV.
Authorities said they were keeping watch at the country’s borders, but police chief Somyot Pumpanmuang told a news conference it was not clear how many people were involved in the attack.
“I don’t suspect one person, I suspect many people,” he said. “I am confident that there are Thais involved but I am not saying it is just Thais or that there are foreigners.”
The government has said the attack was aimed at wrecking the economy, which depends heavily on tourism.
No one has claimed responsibility for the blast. More than half of the dead are foreigners from several Asian countries, and more than 120 people were wounded.
Deputy police chief Jaktip Chaijinda said earlier that investigators believed the man on the video resembled a foreigner more than a Thai.
At least two foreigners have been interviewed in connection with the blast, police said.
Nerves were on edge in the city on Tuesday. A small explosive was thrown from a bridge towards a river pier, sending a plume of water into the air, but no one was hurt.
A government spokesman initially said there were "patterns" linking the two bombs in that both used the explosive TNT, but police chief Somyot said no direct connection between them had been established.
Police Maj Gen Pornchai Suteerakune, commander of the Institute of Forensic Medicine, said the bodies of almost all those killed at the shrine had wounds inflicted by ball bearings packed into the bomb.
The shrine was reopened on Wednesday.
Police spokesman Prawut Thavomsiri said a sketch of the main suspect had been completed and facial recognition technology would be used to try to identify him, but he added that it was possible the suspect was in disguise at the time.
“We believe it is a network and not just one person operating alone. From looking at the CCTV footage we think that the yellow shirt man was maybe operating with one or two other people at the scene,” he added, without elaborating.
Mr Prawut had earlier tweeted that police were offering a 1 million baht (€25,426) reward “to whoever can give information that leads to the arrest of the suspect”.
Police have not ruled out any group, including elements opposed to the military government, for the attack, though they say it did not match the tactics of Muslim insurgents in the south or “red shirt” supporters of the previous administration.
“The attack did not bear the hallmarks of either southern Muslim separatists or red-shirt militants,” said Angel Rabasa, an expert on Islamist militancy at the RAND Corporation.
“Both groups have carried out terrorist attacks in the past, but not on this scale in terms of loss of life.”
He said the attack could be the work of Islamic State, which has been expanding its reach in Southeast Asia, or an al Qaeda-related or independent jihadist group. However, such groups usually claim responsibility for their attacks.
Police said they were also considering the possibility that ethnic Uighurs were behind the bombing.
Thailand forcibly returned 109 Uighurs to China last month.
Hundreds, possibly thousands, of members of the Turkic-speaking and largely Muslim minority group have fled unrest in China's western Xinjiang region, where hundreds of people have been killed, prompting a crackdown by Chinese authorities. Many Uighurs have travelled through Southeast Asia to Turkey.
The blast comes at a sensitive time for Thailand, which has been riven for a decade by a sometimes-violent struggle for power between political factions in Bangkok.
A parliament hand-picked by a junta that seized power in a 2014 coup is due to vote on a draft constitution next month. Critics say the draft is undemocratic and intended to help the army secure power and curb the influence of elected politicians.