Image copyright Thai police Image caption Thai police released this sketch of the man suspected of planting the bomb

Monday's bombing in Thailand was "unlikely" to have been the work of an international terror group, the Thai government has said.

Col Winthai Suvaree, a spokesman for the ruling military junta, said this was the preliminary conclusion reached by investigators.

However, authorities say the prime suspect in the bombings was foreign.

The attack on the Erawan Shrine in central Bangkok on Monday evening killed 20 people and injured scores.

Police say that at least 10 people are suspected of involvement in the attack.

National police chief Somyot Pumpanmuang said he believed the attack was planned at least a month in advance.

Media playback is unsupported on your device Media caption The two men were captured on CCTV standing near the main suspect, in yellow

Analysis: Jonathan Head, BBC News, Bangkok

The latest statement by the Thai authorities casts little new light on the mystery surrounding Monday night's bombing - but it does appear to rule out the involvement of known organisations like al-Qaeda.

The Thais say they have been consulting intelligence agencies from allied countries, and from their discussions they believe the attack is not linked to international terrorism.

That leaves the possibility that it was carried out by local perpetrators, although there is no group in Thailand with a track record that suggests their involvement. Or it may have been the work of a hitherto unknown group.

The Thai police are still looking for three men seen in a grainy security camera video at the shrine just before the blast and have issued an arrest warrant and requested help from Interpol. However, they have no names or nationalities, and it is possible these men are no longer in the country.

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Image copyright AP Image caption Images released by Thai police on Thursday show the main suspect in a tuk-tuk near the shrine before the bombing...

Image copyright AP Image caption ... and riding away from the scene afterwards on the back of a motorcycle taxi

An arrest warrant has been issued for one unidentified man seen on CCTV footage leaving a backpack at the shrine shortly before the blast.

A reward of one million baht ($28,000; £17,950) has been offered for information leading to the main suspect's arrest.

The Thai police have also appealed to Interpol for help in catching the perpetrators.

Media playback is unsupported on your device Media caption Locals will never forget the bombing, but life goes on at the shrine

A motorbike taxi driver who believes he picked up the main suspect said he was having a phone conversation in a language that was neither English nor Thai.

When he was dropped off at a park in the city centre, the suspect "still appeared very calm, just like [a] normal customer. He seemed not in a hurry at all," Kasem Pooksuwan told CNN.

Correspondents say information from the Thai authorities about the investigation has at times been confusing or contradictory.

The fact that the crater at the scene was filled in within 24 hours with a view to getting the shrine reopened as soon as possible has also raised questions around the effectiveness of the probe.

The Hindu shrine is popular with Buddhist and Chinese tourists, but the spokesman said authorities did not believe Chinese people had been the "direct target" of the attack.

Twelve of the 20 dead in Monday's attack were foreigners, including nationals from China, Hong Kong, the UK, Indonesia, Malaysia and Singapore.

Prime Minister Prayuth Chan-ocha has called the bombing the "worst ever attack" on Thailand.

AFP quoted Gen Prayuth as saying he would not attend a memorial service for the victims at the shrine on Friday "on the advice of my security".

"I am not afraid of dying but I am afraid others may die with me as my risk is increasing day by day," he said.

Bangkok explosion