Thai police said on Friday they were looking for a fifth person in connection with a series of blasts in Bangkok blamed on Iranians who may have been targeting Israeli diplomats, as in India and Georgia earlier in the week.
There are more than four people involved in the blasts and we're currently gathering evidence to get an arrest warrant approved, Deputy Police Chief Pansiri Prapawat told a news conference, declining to name the suspect.
It is still unclear whether the suspect is Iranian or not, but he is a Middle Eastern male, he added.
Thai media said the man had been caught on security cameras going in and out of the house rented by the other suspects, last leaving on Tuesday, February 14, a few hours before an apparently accidental explosion there.
One Iranian man, Saeid Moradi, who lost his legs when a bomb he was carrying exploded shortly after, remains seriously ill in hospital. A second, Mohammad Hazaei, is in custody after being arrested at Bangkok's main airport and a third, Masoud Sedaghat Zadeh, is being held in Malaysis after fleeing Thailand.
An Iranian woman, Rohani Leila, is also wanted in connection with the case but is thought to have returned recently to Tehran. She rented the house where the three stayed.
Police Forensic Unit Commander Peerapong Damapong told Thai radio the Bangkok bombs were quite similar to the one used in India and were unlike anything seen in Thailand before.
It's one of those transistor radios that you can carry around, but the insides have been taken out and replaced with C-4, with the head of the bomb consisting of a bolt, a pin and a detonator attached to it, he said.
The explosive had been configured with a five-second delay and a magnet attached to the bomb would allow it to be placed underneath a car, to be activated through pulling on string attached to the pin, he said. Metal bearings in the bomb would have added to the destructive impact.
From what we've seen, it's possible for the components to be bought in Thailand. The explosive isn't that complicated, it's just something that we haven't really seen in this country.
C4, a plastic explosive, is used primarily by the military but is relatively easy to purchase in Thailand.
Thai government and police officials have given conflicting views on the intentions of the Iranians, but Bangkok Police Chief Priewpan Damapong told Thai TV it's clear they wanted to attack foreigners, especially Israeli diplomats.
According to the information and the evidence we've got from the scene, it was the same (type of) bombs as in India and Georgia. There were bombs with magnets being used to attach them to a car, he said.
Police have found no connection between the Iranians and a Swedish man of Lebanese descent, Atris Hussein, a suspected member of Hezbollah, who was arrested in Bangkok on January 13.
He led the authorities to a rented house near Bangkok full of bomb-making material, including more than four tonnes of urea and 10 gallons of liquid ammonium nitrate.
Security experts have expressed concern over Thailand's ability to foil future attacks. With Atris Hussein, Thai officials faced criticism for focusing less on investigating the case than on getting it off the front pages.
Relaxed visa restrictions geared towards Thailand's big tourist industry, combined with ineffective law enforcement, have long made Thailand a haven for foreign criminals.
Bangkok is a city of some 12 million people with sizable populations from many countries, including Iran and Israel.
A European diplomat, who spoke on condition her name and nationality were not revealed, expressed concern about the security situation in Thailand and said the Thai authorities are always downplaying the situation.
If somebody wanted to organise an attack, they could do it easily here. It wouldn't be hard to do something larger than what we saw on Tuesday.
Diplomats' fears are compounded by a separatist conflict in Muslim-dominated southern Thailand, where more than 5,000 people have been killed since January 2004, and where improvised explosive devices -- including increasingly powerful car bombs -- are routinely deployed.
(Additional reporting by Pracha Hariraksapitak, Aukkarapon Niyomyat and Sinsiri Tiwutanond; Editing by Alan Raybould and Sanjeev Miglani)