'Progress', but still no arrests

Thailand's police chief yesterday insisted his officers were making "a lot of progress" in the hunt for the Bangkok shrine bomber despite the lack of arrests and mystery over the attackers' motives.

Speaking after a memorial for the dead at the scene of the unprecedented attack on Thailand, national police chief Somyot Poompanmoung said the bomb was an attempt to stoke fear and uncertainty in the capital.

"The aim is to discredit the government and create a climate of fear to deter tourists," he told reporters.

But he defended the handling of the case despite days of confusing and sometimes contradictory statements from senior police and junta officials.

"There's a lot of progress (in the case), but I can't disclose everything," he said, adding that a reward for information leading to the arrest of those behind the bomb had been tripled to $84,000.

Monday's blast killed 20 people, mostly Asian visitors.

Thailand has asked Interpol for help in finding a man, who was captured on CCTV calmly placing a backpack under a bench at the Hindu Erawan shrine minutes before the blast.