Last Updated Aug 20, 2015 11:53 AM EDT
BANGKOK -- Thailand's military junta said Thursday that this week's deadly bombing in downtown Bangkok that killed 20 people was "unlikely" to have been carried out by international terrorists. Police, meanwhile, said they suspected the plot involved at least 10 people.
Two men who were seen in a security video standing in front of the prime suspect as he removed a backpack and placed it on a bench at the crowded shrine shortly before the blast were cleared as suspects on Thursday. Police had believed they were accomplices.
National police spokesman Lt. Gen. Prawut Thavornsiri said the two men "definitely" were no longer suspects after one of them turned himself in and said he was a tour guide and the other was a Chinese tourist.
Thai authorities have given confusing statements about the investigation, with a military spokesman saying on Thursday they believe the attack wasn't the work of international terrorists - a day after police issued an arrest warrant for the prime suspect that described him as a "foreign man."
"Security agencies have collaborated with intelligence agencies from allied countries and have come to the same preliminary conclusion that the incident is unlikely to be linked to international terrorism," said Col. Winthai Suvaree, the military spokesman.
But when contacted by telephone for clarification, he said that a link to global terrorism hadn't been ruled out. "We still have to investigate in more detail," he said.
Winthai also said on television that Chinese tourists, who were among the victims, were not the "direct target."
The Monday evening attack at the Erawan Shrine, a popular tourist site that is known to attract Chinese visitors, left 20 people dead and more than 120 injured. Four Chinese citizens were among the dead.
No one has claimed responsibility for the blast, sparking a variety of theories into who might be behind it. One is that the blast was a revenge attack related to Thailand's recent deportation to China of more than 100 Uighur Muslims, or that it could have been carried out by Islamist groups expanding their reach in Southeast Asia.
The attack has raised concerns about safety in a city that draws millions of tourists, but life has returned to normal quickly. Subways and shopping malls were bustling and aside from bag inspections at stores and hotel entrances, there was little visible extra security. Authorities say security has been tightened citywide mainly with plain clothed officers.
Police officials told reporters Thursday that authorities believed those behind the blast must have been planned it in advance, maybe a month ahead of time, and likely included a site inspection team, bomb makers, bombers and an escape team. But the comments appeared to be speculative, not based on firm evidence.
"This was a network. We think they would have needed at least 10 people," said national police spokesman Lt. Gen. Prawut Thavornsiri.
Late Thursday, national police chief Somyot Poompanmoung described the number 10 as "theoretical," adding police did not have 10 specific suspects.
So far the firmest clue comes from security camera footage that shows a young man in a yellow T-shirt leaving a backpack at the crowded shrine. Time stamps on the video show he left the temple about 15 minutes before the explosion.
Also Thursday, police doubled a reward for clues leading to the suspect's arrest to 2 million baht, or $56,000, Somyot said. He told reporters that a Thai businessman who wished to remain anonymous had added to the 1 million baht reward police set a day earlier.
Police on Wednesday released a sketch depicting the suspect, a young man wearing glasses with black-bushy hair. The arrest warrant described him as a tall "foreign man" with a fair complexion, a prominent nose and thick lips.
A motorcycle taxi driver believed to have driven the suspect away from the scene told police the suspect handed him a piece of paper saying "Lumpini Park," a nearby park, and was talking on the phone in a foreign language that was not English, Prawuth said. But they don't have any indication what language it was.
Among the 20 people killed, Thai authorities have identified six victims as Thai and four as Malaysians, along with four Chinese, two people from Hong Kong including a British citizen, one Indonesian and one Singaporean. Two victims remain unidentified.
Bangkok has seen politically charged violence in the past decade. In 2010, more than 90 people were killed in two months of violence that was centered on the same intersection where Monday's bomb went off. But none of those attacks included a bomb that seemed intended to produce mass casualties.
Thailand has seen many violent attacks in recent years, particularly in a long-running insurgency by Muslim separatists that has killed over 5,000 in the country's south. Those attacks, however, have never reached the capital.