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

Video footage has emerged of a key suspect police want to question in connection with the deadly bomb blast in the Thai capital, Bangkok.

The footage, from a CCTV camera, shows a man in a yellow shirt leaving a backpack in the Erawan Hindu shrine.

At least 20 people died in Monday's blast, about half of them foreigners, and more than 120 were injured.

In a separate attack on Tuesday, an explosive device was thrown at a pier in Bangkok, but no-one was hurt.

Nationals from China, Hong Kong, the UK, Indonesia, Malaysia and Singapore are among the foreigners killed in the attack.

Media playback is unsupported on your device Media caption Mobile phone footage shows the moment of Monday's bombing in Bangkok

CCTV footage of a suspect wanted for questioning

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Still images of the suspect had already been released.

In the new footage, he is shown carefully and deliberately removing his backpack inside the shrine, getting up without it and immediately leaving the scene.

The spot where he was sitting is precisely where the bomb went off a few minutes later, says the BBC's Jonathan Head in Bangkok.

"There is a suspect... we are looking for this guy," Prime Minister Prayuth Chan-ocha told reporters.

Authorities were "quite close" to identifying the suspect, Thai government spokesman Maj Gen Weerachon Sukhontapatipak told the BBC, but other leads were also being pursued.

He said no motive was being ruled out, but that the bomber did not appear to be Thai and the character of the bombing was "quite different" from previous bombings by southern Thai insurgents.

He said security at transport hubs and tourist sites was being beefed up.

Bangkok explosion

Bangkok Bangkok Bangkok Gaysorn Plaza shopping centre Erawan Shrine Erawan Shrine BTS Skytrain Approximate blast area Ratchaprasong Junction 200m Google Reuters 500 feet THAILAND

The bomb was detonated at about 19:00 local time (12:00 GMT) on Monday when the shrine, and the nearby Ratchaprasong junction, were crowded.

Mr Prayuth called it the "worst ever attack" on Thailand.

"There have been minor bombs or just noise, but this time they aim for innocent lives. They want to destroy our economy, our tourism."

Image copyright EPA Image caption Divers retrieve pieces of a device thrown at a pier in Bangkok on Tuesday

In Tuesday's incident, a device was reportedly thrown at the busy Sathorn pier in Bangkok. It landed in water where it exploded harmlessly, but police said it could have caused many injuries.

Maj Gen Weerachon said there were similarities between Monday's deadly blast and the explosion on Tuesday, but the authorities had not established links between the two.

"Both were TNT bombs," he told reporters. "There's a pattern, but we have not yet found links."

Monday's bomb was clearly placed to cause maximum casualties, says our correspondent in Bangkok.

In currency trading, the Thai baht fell to its lowest level in six years over concerns about the impact on tourism.

Analysis: Pavin Chachavalpongpun, Center for Southeast Asian Studies, Kyoto University

There are suggestions this could be related to the Muslim separatist conflict in southern Thailand, but the political violence has been limited to the three southern provinces - never the capital.

Others have mentioned the Muslim Uighur minority in China. They are unhappy that Thailand deported Uighur refugees back to China, where the minority complain of persecution, and might have wanted to punish the Thai state, the thinking goes. But we don't know enough at this point to support this theory.

However, international terror networks usually claim responsibility quickly after the incident, which hasn't happened in this instance so far.

One thing is clear - this is a failure of the government's intelligence work.

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National police chief Somyot Poompummuang described the device as a 3kg (6.6lb) pipe bomb - an improvised device where explosive material is put in a sealed cavity to maximise the explosive impact.

"The impact was so strong it sucked us forward and then pushed us back," one witness, Leify Porter, from Australia told the BBC.

She said she had seen "very graphic" scenes at the site of the explosion.

Media playback is unsupported on your device Media caption Dashcam footage captures the moment the bomb exploded near a shrine

Media playback is unsupported on your device Media caption It is not known if Tuesday's pier explosion is linked to Monday's blast

Erawan shrine is dedicated to the Hindu god Brahma, but is also visited by thousands of Buddhists each day.

It sits between a five-star hotel and a popular shopping centre on the Ratchaprasong intersection, which has been the centre of political demonstrations in recent years.

Image copyright EPA Image caption Authorities believe foreign tourists were the target - but most of the dead and injured are Thai

Image copyright Getty Images Image caption Forensic evidence has been collected and a clean-up operation is under way

Image copyright AP Image caption Many bereaved are now facing the grim task of identifying the remains of loved ones

Bangkok has seen a decade of sometimes violent rivalry between political factions.

The military took over the country in May last year, removing an elected government following months of unrest. The capital has been relatively calm since then.