One man has been arrested over an alleged bomb plot that has caused 11 countries to issue travel warnings to Thailand

Police are hunting a terror suspect believed to be at large in Bangkok after the arrest of a man in an alleged bomb plot that has so far forced 11 foreign embassies to issue travel warnings to Thailand.

The national police chief, General Priewpan Damapong, said the suspected bomb plotters – two Lebanese men thought to be linked to pro-Iranian Hezbollah militants – called off the scheme after police caught wind of the plot and arrested one of them on Thursday.

Thai police – who are warning visitors in tourist-heavy areas such as Khao San Road to exercise caution – believe the suspect is in Bangkok but are also upping security searches in nearby provinces and other popular tourist destinations such as Pattaya and Phuket.

Thailand's metropolitan police spokesman Piya Ayutho said: "From intelligence reports, the attackers will use explosives, so the public is urged to be vigilant in risk areas, or in buildings visited by a lot of foreigners, and to particularly look for vehicles that have been left in certain areas for a long time."

The prime minister, Yingluck Shinawatra, said she had ordered the Thai army, police and security forces to remain vigilant and inform her of any developments, according to the Bangkok Post.

Sketches released late on Friday night by Thai police showed the suspect as a white Middle-Eastern man with short hair and stubble, around 1.8m (5ft 9in) tall. Anyone who believes they have seen the suspect is urged to report to the nearest police station or call 191 from within Thailand.

Priewpan said the man in custody, a Swedish national of Lebanese origin identified as Attiris Hussein, told police an attack had been planned but was called off when police learned about it. Hussein was detained by police on Thursday at Bangkok's Suvarnabhumi international airport while trying to leave the country.

Authorities said charges had not been pressed against Hussein because of lack of evidence that he had committed an offence.

According to the Bangkok Post, Hussein told Thai officials that although he was a member of Hezbollah, he was not a member of the group's militant arm.

The alleged bomb plot, combined with Hussein's arrest, caused many foreign embassies, including those of the US, UK and Israel, to issue travel alerts for Thailand, warning that foreign terrorists could be planning to launch attacks in tourist areas in Bangkok in the near future. The US called the threat "Bangkok-specific" and "credible".

The warnings upset Thai authorities, who were withholding the news "since it could have an impact on tourism and cause panic among citizens", according to the defence minister, Yuthasak Sasiprapha.

Thai security agencies said they had known of the terrorist plot since December and had since been tracing a group of suspects thought to be involved.