Police have charged a Swedish-Lebanese man with suspected links to the Hezbollah militant group with possession of prohibited substances after they found a huge cache of materials used for making explosives in Samut Sakhon's Muang district Monday.
The Swedish passport used to enter Thailand and carried by Mr Atris when he was arrested last week.
More than 200 police Monday raided a three-storey commercial building in the Mahachai area after Hussein Atris, a Lebanese man carrying a Swedish passport, was arrested at Suvarnabhumi Airport on Thursday evening.
National Police chief Priewpan Damapong said 4,380kg of urea-based fertiliser and 290 litres of ammonium nitrate were found on the second floor of the building.
The police also discovered many pairs of slippers, A4 paper and 400 electric table fans on the ground floor.
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The suspect had told police that explosive materials were hidden there, Pol Gen Priewpan said.
Mr Atris told investigators that the materials were not intended for use in any planned attack in Thailand.
The components were concealed inside boxes for shipping to other countries, Pol Gen Priewpan said.
He said the suspect had rented the building for more than a year and the materials had been hidden in the building for quite some time.
The urea-based fertiliser and ammonium nitrate will be kept at the Royal Thai Police's Quartermaster Division for further inspection.
After the police raid in Samut Sakhon Mr Atris was taken to the Border Patrol Police Bureau on Phahon Yothin Road for questioning.
Assistant national police Charamporn Suramanee said possession of urea-based fertiliser is not against the law, but ammonium nitrate is a controlled chemical substance under the Arms Control Act of 1987.
Pol Lt Gen Charamporn said the penalty for possession of ammonium nitrate without permission from the Defence Ministry is a five-year prison term and a fine of 50,000 baht.
Mr Atris has been charged with possession of a prohibited chemical substance in violation of the arms control law, Pol Lt Gen Charamporn said.
Metropolitan Police Bureau chief Winai Thongsong said Mr Atris was sent to the Immigration Police Bureau for holding last night and police may today seek court approval to continue his detention for further interrogation.
Undated Royal Thai Police handout photo of alleged Hezbollah member Atris Hussein.
Mr Atris will remain in police custody and the national police chief will make any ultimate decision on any possible extradition and deportation.
A source at the Immigration Bureau said the US wants to use Thailand as a base to destroy terrorist networks, which would not benefit Thailand.
The source said the arrest of the Lebanese-Swedish suspect was at the behest of Israeli authorities.
Thailand actually could have revoked the suspect's visa and deported him straight away.
But as it happened, the suspect was held in detention because the US wanted him detained, which could spell trouble for Thailand.
"When the suspect was arrested, he was not deemed guilty of any offences.
"But police now have to detain him after the US issued a warning about possible terror attacks in Bangkok, which became big news," the source said.
The source said the US wanted the suspect and wanted to use Thai law to investigate and expand terrorism investigations, although Thai police had not determined if Mr Atris was linked to any terrorist network. The source also questioned if the seizure of the explosive materials in Samut Sakhon was a set-up to further detain Mr Atris in Thailand.
Meanwhile, Prime Minister Yingluck Shinawatra has urged the United States to immediately revoke its terrorism warning in light of Mr Atris' arrest.
Defence Minister Yutthasak Sasiprapa quoted Ms Yingluck as saying the warning, if prolonged, will damage the country.
Gen Yutthasak said the issue had been discussed at a one-hour meeting between Gen Nipat Thonglek, director of the Defence Ministry's Policy and Planning Office, and Col Edward Swanda, chief of the Joint US Military Advisory Group Thailand.
US embassy spokesman Walter Braunohler said the terrorist warning for American citizens has remained valid despite Mr Atris' arrest.