Image copyright Thai police Image caption Thai police released this sketch of the "man in yellow", suspected of planting the bomb

Thailand has trebled its reward for information leading to the arrest of the main suspect in the deadly bomb attack on the Erawan Shrine in Bangkok.

Police are hunting for a man seen dropping off a backpack shortly before an explosion ripped through the popular site on Monday, killing 20 people.

Thai PM Prayuth Chan-ocha said progress was being made in the investigation.

A multi-faith memorial to the victims of the attack was held at the shrine on Friday.

Little evidence has emerged from the attack, which Prime Minister Prayuth called Thailand's worst-ever.

Bangkok bomb attack

Image copyright Thai police/Khao sod Image caption CCTV footage from the night of the blast shows what police have called the main suspect in a yellow shirt and black bagpack

Police released a sketch and video of their main suspect, who has been described as foreign and is believed to have been working as part of a network.

The reward for the wanted man now stands at three million baht ($84,000; £53,600).

In his weekly address to the nation, Prime Minister Prayuth said he would "expedite all investigations to bring perpetrators to justice".

The attack aimed to "discredit the government and create a climate of fear to deter tourists," said the Thai police chief, Somyot Poompanmoung.

He also played down his earlier suggestion that as many as 10 people might have been involved.

Image copyright EPA Image caption The victims of the attack have been remembered at a multi-faith ceremony

Image copyright EPA Image caption The shrine, which is particularly popular among Chinese tourists, has reopened for visitors

At the Erawan Shrine on Friday, doves were released at a memorial ceremony attended by Buddhist, Muslim, Christian, Hindu and Sikh leaders.

One of the organisers said it was to remember the victims, but also "to tell tourists that we will try to protect you who will be coming here in the future all the best we can".

Various theories abound about what motivated the attack, from internal political unrest to insurgents in the south, although the Thai authorities say it is unlikely to be the work of an international terror group.