National police chief Somyot Poompunmuang said Sunday police have identified "a group of suspects" in last Monday night's bombing at the Erawan shrine, but refused to discuss details, including whether he thinks the attackers are Thais or foreigners.
He admitted progress in the investigation was slow, but denied it was from police performance, and blamed outdated equipment.
The national chief vowed to try to procure more equipment to boost police capacity.
"We will only receive assistance in terms of equipment, but will not allow any representatives from other countries to interfere in our investigation," said Pol Gen Somyot. He insisted police have not yet ruled out any motives.
He said although foreigners are involved in the attack, this does not mean they are part of a transnational criminal network.
The police chief said the attack may have been carried out by people with different views, but insisted he was not necessarily referring to religious beliefs.
Metropolitan Police Bureau chief Sriwara Rangsipramanakul said the probe into the shrine blast has made steady progress.
A taxi driver, who carried the bomb suspect from the Yannawa area to Hua Lamphong railway station before the suspect took a tuk-tuk to the Erawan shrine, has been brought for questioning, Pol Lt Gen Sriwara said, though he refused to discuss the driver's account.
A source said police are looking for another taxi driver who picked up the suspect from Silom Soi 9 after the explosion.
Police on Sunday questioned about 15 taxi drivers whose taxis were captured by CCTV cameras around that time.
The MPB chief conceded it is difficult to say whether the suspect has fled the country.
Meanwhile, Phra Phrom Methi, the Sangha Supreme Council (SSC) spokesman, said a commemoration and prayer for Erawan blast victims, planned for today at 5.30pm in front of the Amarin Plaza at Ratchaprasong intersection, has been postponed for safety reasons.
Pol Gen Somyot had asked the SSC to postpone it because the government is still worried about the situation.
Responding to a Japanese media report that the shrine bomber is a Spanish national, Pol Lt Gen Sriwara said he had not heard of the report.
Meanwhile, police spokesman Prawut Thawornsiri said police have not yet confirmed whether a man with a blue T-shirt seen in CCTV footage kicking a package into water at the Sathon pier around 7.20 pm on Monday, less than 30 minutes after the Erawan shrine blast, is also a would-be bomb attacker.
CCTV cameras have captured the route on which the man was travelling, the spokesman said.
Pol Lt Gen Prawut said the man at the Sathon pier is likely to be an Asian person.
Meanwhile, Pol Gen Somyot launched an operation to search for criminals in Bangkok.
More than 1,000 police, army soldiers, City Hall staff and civilians took part in the operation, aimed at boosting public confidence.
More than 3,550 dwellings, including condos and tourist guesthouses, were searched, but turned up no bombing clues.