Thai authorities have arrested a Lebanese man with suspected links to Hezbollah militants, after receiving a warning from Israel.
The arrest came hours after the US advised its citizens in the Thai capital, Bangkok, to be on the alert over a possible terrorist threat.
Deputy Prime Minister Chalerm Yoobamrung said one man was being held over possible immigration offences.
The situation was now under control, he said, and urged people not to worry.
"Following concern raised by the Israeli embassy about a possible attack by a group of Lebanese terrorists in Bangkok, Thai police officials had been co-ordinating with Israeli officials since before the New Year," Reuters news agency quoted Mr Yoobamrung as saying.
He told the Associated Press news agency police had been tracking the two men and called one in for questioning.
"Technically the two men have not committed any crimes under the Thai law, so we could only use the immigration law to keep this one suspect in custody," he said.
An official at the defence ministry told Reuters that Israel had contacted them on 22 December with information that two or three suspects could be planning an attack in Thailand, but that those individuals had left the country. A second warning came on 8 January, he said.
Israel's foreign ministry declined to comment on the reports.
Hezbollah is a Shia Islamist movement which holds several seats in Lebanon's parliament as well as being the country's most powerful military force. Its defining platform is hostility towards Israel.
The movement is backed mainly by Syria and Iran and is considered by the US to be a terrorist organisation.
The US embassy in Bangkok issued a warning on Friday that Americans should "exercise caution when visiting public areas where large groups of Western tourists gather".
It said they should "keep a low profile in public areas, particularly areas frequented by foreign tourists", without giving further details of the potential threat.
The Thai authorities had said there was no need for a general alert as it would "cause panic and affect our tourism".
Bangkok has been hit by several small scale bombs in recent years in what are thought to have been politically motivated attacks, and Thai Islamist insurgents regularly carry out attacks in the southern provinces.
But attacks on or by foreigners are rare.