Police investigators believe two other suspects may have been involved in the bomb blasts that shook Sukhumvit Soi 71 on Tuesday.
A security officer uses a Segway to cover more ground around the sprawling Suvarnabhumi Airport as security is tightened further. PATIPAT JANTHONG
National deputy police chief Pansiri Prapawat said authorities are now seeking to arrest a man they have identified as 52-year-old Nikkhahfard Javad who was seen on surveillance tapes in the area of a Sukhumvit 71 home just before an explosion ripped through it on Tuesday afternoon.
Police so far have sought arrest warrants for four people related to the bomb blasts. They are suspected to be part of a team of Iranian nationals targetting Israeli diplomats in Thailand.
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Materials found in the blast, including C4 explosives and magnets to secure the bombs to cars, were similar to those used in attacks earlier this week against Israeli diplomats in India and Georgia.
Two Iranians are in Thai custody. Saeid Moradi, 28, was injured in one bomb blast and is being treated at Chulalongkorn Hospital, while Mohummad Khazaei, 42, was detained at Suvarnabhumi airport hours after the incident just as he was boarding a plane bound for Malaysia.
Masoud Sedaghat Zade, 31, the third Iranian thought to have been involved, was arrested in Kuala Lumpur on Wednesday. A suspected female accomplice, Leila Rohani, is being sought for questioning. Immigration records show she left Thailand earlier this month for Iran.
Javad: Fifth suspect seenat Sukhumvit71
Pol Gen Pansiri said police have submitted evidence to prosecutors seeking the extradition of Mr Zade from Malaysia.
Malaysia Home Minister Hishammuddin Hussein told the Bernama news agency the country was "prepared to cooperate fully in the situation".
Malaysian security officials said Mr Zade had made several trips to Malaysia in the past several months.
Mr Zade told interrogators he was an auto parts dealer and that he had visited Malaysia, Thailand and other countries in the region on business.
Prime Minister Yingluck Shinawatra may discuss the extradition request with Malaysian Prime Minister Najib Razak when she visits Kuala Lumpur on Monday.
Pol Lt Gen Winai Thongsong, the Metropolitan Police Bureau commissioner, said police may have also identified a sixth suspect related to the bombings.
The person, whom he declined to identify, was seen with Ms Rohani when she rented the Sukhumvit 71 home.
Pol Lt Gen Winai said police had been put on alert, particularly in areas frequented heavily by Middle Eastern tourists including the Nana area on Sukhumvit Road and Khao San Road.
Bangkok Governor Sukhumbhand Paribatra, speaking after a briefing with police and security forces, said the entire city should be on alert for attacks.
He said it is "inappropriate" to single out people from the Middle East or intensify surveillance solely in tourist-populated areas.
"The explosions didn't take place in an area where foreign tourists stay. We should maintain a watch across the entire city and keep an eye open for anything suspicious," he said.
MR Sukhumbhand said private surveillance cameras would be integrated into the city surveillance network to strengthen security.
The Bangkok Metropolitan Administration, which now operates 15,000 cameras in the city, will install another 10,000 cameras this year.
Deputy Prime Minister Yutthasak Sasiprapa said authorities would conduct the investigation in a clear, speedy and transparent manner.
"We will speed things up and try to clear things. We are friends with both Iran and Israel," he said.
Gen Yutthasak expressed support for proposals to tighten visa regulations, saying the Foreign Ministry has begun reviewing the issue.
"We need tourists to help boost the economy, but we have to start keeping an eye on them," he said.
Immigration authorities said the four confirmed suspects had made multiple trips to Thailand over the past year under tourist visas.
The presumed terror attack unravelled on Tuesday afternoon when an explosion occurred at the Sukhumvit 71 home. The occupants fled the house and Mr Saeid threw two bombs during his escape, injuring four bystanders and blowing off his own legs when one bomb bounced back at him.
Investigators later found two complete bombs packed with radios with 2 kilogrammes of C4 each.
Iran, which is already facing international condemnation over its nuclear programme with allegations it is trying to make nuclear weapons, has denied any involvement in the bomb plot.
But Israeli Vice Prime Minister Moshe Yaalon named Brigadier-General Qasem Soleimani, commander of the Quds Force, a covert arm of Iran's Revolutionary Guards Corps, as the mastermind of the attacks.
"We see what is happening in India, Georgia and Thailand. It is the same pattern. The same bomb, the same lab, the same factory," Mr Yaalon said in a newspaper interview.
Will Hartley, head of the Terrorism & Insurgency Centre at IHS Jane's, said Israel's assertion of an Iranian link was "not unreasonable given the circumstantial evidence".