Police said they detained a Lebanese man with suspected ties to Hezbollah, after the US Embassy issued an emergency warning to its citizens to beware of a "real and credible" terrorist attack in Bangkok on Friday.
Deputy Prime Minister Chalerm Yubamrung said authorities received a tip-off before New Year's Eve celebrations of a planned attack, which was apparently to target Israelis.
"At first we were told the Palestinians were behind it but it turned out to be the Hezbollah," a Lebanon-based Shiite militant group backed by Iran.
He said police detained on Thursday a Lebanese suspect with alleged links to Hezbollah.
Authorities had been "following two Lebanese men and called in one of them ... for questioning," Mr Chalerm said.
The US Embassy message said that "foreign terrorists may be currently looking to conduct attacks against tourist areas in Bangkok in the near future." It urged Americans to "keep a low profile" in public and to exercise caution in areas where Western tourists gather.
EARLIER REPORT
United States authorities had informed the Thai government that two suspected Muslim terrorists had entered Thailand, Defence Minister Yutthasak Sasiprapa said after the US embassy on Friday alerted its citizens to possible terrorist attacks in Bangkok.
"The US contacted us last night about two terrorists who had entered Thailand and plan terrorist activities," Defence Minister Yutthasak Sasiprapha told reporters.
"Our intelligence officials are working closely with the US and following the terrorists' movements closely. I believe we will arrest them tonight," he added.
"For Thai citizens, there is no need to announce any warning because it will cause panic and will affect tourism."
The US embassy said in a messaged posted on its website on today that "foreign terrorists may be currently looking to conduct attacks against tourist areas in Bangkok in the near future."
"US citizens are urged to exercise caution when visiting public areas where large groups of Western tourists gather in Bangkok," it said.
The embassy's travel warning urged its nationals to stay alert when going out and to report any suspicious objects or activities to authorities.
"This message alerts US citizens in Thailand that foreign terrorists may be currently looking to conduct attacks against tourist areas in Bangkok in the near future. US citizens are urged to exercise caution when visiting public areas where large groups of Western tourists gather in Bangkok.," it said.
"We also encourage you to keep a low profile in public areas, particularly areas frequented by foreign tourists."