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Flowers, notes and a placard are seen at the Erawan shrine, the site of Monday's deadly blast, in central Bangkok, Thailand, August 20, 2015. International terrorists were not suspected of the bomb attack in Bangkok this week that killed 20 people and China was not the target, Thai authorities said on Thursday, as police said they believed at least 10 plotters were involved. REUTERS/Athit Perawongmetha

Thai Police are now on the hunt for a "woman wearing a black shirt" as a potential suspect involved in the deadly bombing at Bangkok's Erawan Shrine.

"I would urge her to come forward to provide information to police.” Lt. Gen. Prawut Thavornsiri said.

According to a senior police spokesman, the hunt began on Thursday after authorities confirmed they had cleared two international suspects of their involvement in the Bangkok bombing .

According to the government-run National News Bureau of Thailand, police have also doubled the reward to THB $2 million (approximately A$76.6k) for any information on the suspect that would result in his arrest.

Among the two men arrested, one was a tourist and the other a tour guide. They were taken into custody by the Thai police after the colours of the shirts they were wearing at the shrine matched the CCTV footage of the blast.

Col. Decha Promsuwan said the police failed to find any established links of the blast with the men after completing their interrogation at the metro police headquarters. Thai authorities believe that at least 10 people have been a part of the bombing that rocked Central Bangkok on Monday.

"This operation was carried out by a big network,” Royal Thai Police Commissioner Gen. Somyot Poompanmoung said. "There must be a preparation for materials and explosives.”

Col. Winthai Suvaree, a spokesman for Thailand's ruling military junta, said that the police belief that at least one foreigner was involved in the bombing might be wrong as the operation is unlikely to be linked to international terrorism.

At the moment, police are mainly looking for a suspect who was caught on the CCTV footage hiding a backpack under a bench near the shrine minutes before the bomb exploded. They are also involved in searching for two other men who appeared on the CCTV footage and are suspected of working with the chief suspect.

Meanwhile, Thai security forces have sought help from global police organisation Interpol and intelligence agencies from allied countries, officials confirmed.

Police spokesman Prawut said the authorities are clueless of the main suspect’s whereabouts. He said investigators are involved in reviewing surveillance video from two international airports at Bangkok as well as from the scene of the bombing.

A Thai taxi driver has come forward with information of a man, who he believes to be the suspect. The driver named Kasem Pooksuwan said that he picked up the suspect after the blast took place and assured that he wasn’t a Thai as he spoke an unfamiliar language on his cell phone while on the taxi, reported CNN.

Pooksuwan also told CNN the man showed him a piece of paper with the name of a central city park written on it in English without speaking to him. "When I dropped him, he still appeared very calm, just like (a) normal customer. He seemed not in a hurry at all," he added.

CCTV footage was shared this week showing a man in a yellow T-shirt, possibly the suspect, sitting on a bench near the shrine and taking off a large, black backpack. Watch the footage, courtesy of The Guardian, here:

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