BANGKOK (Reuters) - Nearly a week after a bomb in Thailand killed 20 people, authorities appear no closer to identifying suspects or a motive, with police saying on Sunday a lack of modern equipment was hampering their investigation.

The blast last Monday at one of the capital's most famous shrines, packed with Asian visitors, will inevitably dent the tourist industry, one of the economy's few bright spots.

Economic woes could undermine the military government as it steers the country towards an election next year under a new constitution critics say will not end a decade of turbulent politics.

The strongest evidence appears to be grainy CCTV footage of a young man who left a backpack at the Erawan Shrine before the explosion. He disappeared into the night, on a motorcycle taxi.

Authorities have issued confusing and at times contradictory statements about the suspect's appearance, the number of accomplices he might have had and the likelihood of foreign involvement.

National police chief Somyot Pumpanmuang said progress was being made but a lack of equipment was a problem.

"We don't have modern tools to support our work ... we have difficulties with technology and data," he told reporters, without elaborating. "We have to wait for cooperation from abroad, to come and help with this equipment."

Police are also investigating another piece of CCTV footage that could provide clues to who was responsible for a small blast on Tuesday at a river pier that caused no injuries.

Police said they were investigating the footage of a man who appeared to push a bag off a walkway into the river. They have not confirmed the blasts were linked.

The Erawan Shrine, dedicated to a Hindu deity, is hugely popular with tourists from Chinaand seven of the 14 foreigners among the dead were from mainland China and Hong Kong.

Police initially speculated Muslim ethnic Uighurs from western China might have been responsible but officials later cast doubt on an international link and said China was not targeted.

Muslims waging a low-level insurgency in southern Thailand have never been known to carry out such an attack and neither have activists from a decade-long struggle for power between the establishment and populist former premier Thaksin Shinawatra.

The government has offered $85,000 for information leading to the arrest of the bomber and the family of the self-exiled Thaksin has offered $200,000, the Bangkok Post reported.

As the hunt for the bomber went on, authorities said two people had been arrested for spreading "confusing information" on social media.

(Additional reporting by Viparat Jantraprapaweth; Writing by Robert Birsel; Editing by Clarence Fernandez)