Thai police said on Monday the trail had gone cold in the hunt for a bomber a week after 20 people were killed in the country's worst bomb attack, and they were unsure if the main suspect was still in Thailand.

Faulty security cameras and a lack of equipment were hampering the investigation while an explosive device found at a building site on Monday proved a false alarm, not connected with the Aug. 17 attack on Bangkok's most famous shrine.

The main evidence police have for the blast at the Erawan Shrine to a Hindu deity popular with Asian tourists, is security camera footage.

Some of it shows the suspected bomber leaving a backpack and walking away. The young man with a yellow shirt and dark hair was also caught on closed circuit television camera leaving the scene on the back of a motorcycle taxi.

But after that, there was very little, police said.

"In terms of the CCTV cameras, some don't capture images properly and some were damaged which is a waste of time for police piecing together where the suspect went," national police chief Somyot Poompanmuang told reporters.

"You want the truth? We don't know if the suspect is still in Thailand but I have to assume he still is because we've got no information that he left."

Somyot said on Sunday a lack of modern equipment was hampering the investigation and he was seeking foreign help.

The government said the attack was aimed at undermining the economy by hurting the tourism industry as growth flags in other sectors.

Half the 14 foreigners killed were from mainland China or Hong Kong, but the Thailand-China Tourism Association, which oversees more than 200 operators bringing Chinese visitors, said there was little sign Chinese holidaymakers had been put off.

China is Thailand's biggest source of tourists.

"There have been maybe one or two cancellations here and there. Nothing major," association president Ronnarong Cheewinsiriamnuai told Reuters.

Chinese operators had not canceled flights, Ronnarong said, adding he had seen a dip of about 2 percent in Chinese visitors.

The military government wants stable growth as it steers the country towards an election next year under a new constitution critics say will not end a decade of turbulent politics.

Earlier, police said they had defused a bomb at a construction site but later said it was a small, old explosive not believed connected to the shrine blast and a second explosion at a pier on Bangkok's river the next day that caused no casualties.

A Ministry of Information spokesman said six provincial government websites had been hacked by a group called the 'Fallaga Team', who said they were Muslims from Tunisia, but said the hackers did not get access to government data.

Police said the hacking was not believed to be related to the bomb attack.