Thai authorities said Friday they had detained a Lebanese man with suspected links to the Hezbollah militant group, after the United States warned of a terrorist threat against tourists in the kingdom.

"Foreign terrorists may be currently looking to conduct attacks against tourist areas in Bangkok in the near future," the US embassy in Bangkok said in an emergency message posted on its website.

"US citizens are urged to exercise caution when visiting public areas where large groups of Western tourists gather in Bangkok."

A Thai senior intelligence officer who did not want to be named told AFP that the kingdom had been informed before the New Year by Israel of a possible threat.

The suspect was detained Thursday while the other man had already fled the country, he said.

Thailand's Deputy Prime Minister Chalerm Yubamrung told AFP by telephone that the detained suspect was being questioned by the Thai authorities.

"We already have one suspect in custody for interrogation at a government building in Bangkok. He is a Hezbollah from Lebanon," he said.

"I want to assure people that there is nothing to worry about. The police will take care of the situation and everything will be under control."

Hezbollah, an Iranian- and Syrian-backed Muslim Shiite group, is blacklisted as a terrorist organisation by Washington and currently dominates the Lebanese government.

"Israel was suspicious that these two men might be terrorists, so they gave information, including their names, to our police before the New Year," the senior intelligence officer said.

The suspect has denied involvement with any terrorist activities, he added.

"These two men entered Thailand a while ago but did not conduct any terrorist activity. I wonder why Israel was suspicious about them."

The warning is another blow to Thailand's tourist-friendly image, which was badly dented last year by devastating flooding across much of the country, as well as rounds of rival political protests in recent years.

In 2008 a nine-day blockade by "Yellow Shirt" protesters stranded tens of thousands of travellers, and the industry was badly hit again in 2010 during "Red Shirt" street demonstrations.

Bangkok's central shopping area was reduced to a battle zone during an army crackdown on the rallies, and more than 90 people were left dead.

An eight-year-old shadowy insurgency continues to plague the country's Muslim-majority deep south, but the rebels have never been known to attack outside of the region.

The insurgents are not thought to be part of a global jihad movement but rather are rebelling against a long history of perceived discrimination against ethnic Malay Muslims by governments in the Buddhist-majority country.

Prime Minister Yingluck Shinawatra also told reporters that authorities in the kingdom had the current situation under control.

"I would like to tell our people and tourists that there is nothing to worry about," she said.

In the most prominent terrorist attack in Southeast Asia in recent history, 202 people -- most of them foreign tourists -- were killed in 2002 by bombings on the Indonesian island of Bali.

In August 2003, alleged mastermind Riduan Isamuddin, an Indonesian known as Hambali, was arrested in Thailand.

He was suspected of being Al-Qaeda's representative in Southeast Asia and operational chief of Southeast Asian militant group Jemaah Islamiyah.