Staff members clean the explosion site at the Erawan Shrine in Bangkok, Thailand, Aug.18, 2015. The death toll in the blast Monday night has risen to 20, police spokesman Prawut Thawornsiri said. Four Chinese nationals,including two from the Hong Kong Special Administrative Region,have been confirmed killed in a Bangkok explosion Monday night, the Chinese embassy in Thailand said on Tuesday. (Xinhua/Li Mangmang)

BANGKOK, Aug. 19 -- A man who left a backpack at the scene of Monday's deadly bombing in central Bangkok is now the focus of the hunt for the bomber, said police.

Twenty people were killed and more than 100 others injured in the explosion at Erawan Shrine, a popular tourist destination in downtown Bangkok, at about 7 p.m. local time (1200 GMT) on Monday.

In a videa footage revealed by the police, a man wearing a yellow T-shirt, who appeared young, walked into the shrine with a backpack, which he later left underneath a bench.

He walked out of the shrine without the backpack. Three minutes later, the explosion took place.

The man left the scene aboard a motorcycle taxi, said National police spokesman Prawut Thavorn.

"It is quite clear that he is the perpetrator in this case," Prawut told local television station Channel 3, adding that police were also trying to track down the motorcycle taxi driver.

More victims were identified on Tuesday. China said six of its nationals, including two from the Hong Kong Special Administrative Region, had been confirmed among the dead.

Another 22 Chinese, including 17 from Chinese mainland, two from Hong Kong and three from China's Taiwan, were receiving treatment in hospitals, said the Chinese Embassy in Thailand, adding more than 10 other Chinese, who sustained minor injuries, have been discharged from hospital.

One Chinese remained missing after the blast, according to the embassy.

Meanwhile, the Malaysian government said that two more of its citizens were killed in the blast, raising the number of Malaysian fatalities to four.

Singapore also confirmed one national was among those killed in the attack.

Thai Prime Minister Prayut Chan-o-cha on Tuesday vowed to expedite all investigative efforts to find perpetrators of the explosion and bring them to justice.

"From this incident, it is apparent that there are active individuals or groups that harbor the intention to damage Thailand, who may be pursuing political gain or other intentions by damaging the economy and tourism," Prayut said.

For foreign nationals residing in Thailand, including embassies, consulates and international organizations, he pledged to safeguard the security of their life, property, and interests.

Prayut also asked for cooperation from the media, including all social media agents, "in providing news that will be constructive rather than news which expounds violence and destruction, which may have a misleading effect on ongoing investigations and create misunderstandings in our society."

In a statement on Tuesday, the United Nations World Tourism Organization (UNWTO) strongly condemned the attack, syaing it felt "deeply saddened and shocked by the attack."

"On behalf of the global tourism community, UNWTO offers its heartfelt condolences to the families and friends of the victims and reiterates its full support to the people and the Government of Thailand," the statement said.