An armed group was plotting car bomb attacks in a province near Bangkok, Thailand’s national security head said on Tuesday.

“The deputy prime minister instructed security agencies [to] closely track and monitor anything unusual including things used to prepare bombs and cars,” said Thawip Netniyom, Thailand’s chief of national security.

“Why target Bangkok? They probably want to make an impact,” he said, without giving details on which groups could be behind the plot.

Thailand, a popular tourist destination, has seen a series of bomb attacks in the country’s south over the past few weeks, including a wave of bombs in tourist towns on 11-12 August that killed four Thai people and injured dozens including foreigners.

Police have linked the attacks to Muslim separatists operating in Thailand’s far south.

Security chief Thawip said he was not sure whether the planned car bombs and the August attacks were related.

Thailand’s tourism industry accounts for 10% of gross domestic product but has weathered more than a decade of unrest including two military coups and the recent bombings.

Britain’s foreign office advised travellers to exercise caution following the August bombings.

In August 2015 a bomb ripped through a religious shrine in Bangkok killing 20 people, most of them tourists. But the attack failed to seriously dent tourist arrivals.

Two ethnic Uighur Muslims from China are on trial in Thailand accused of carrying out the attack.

Analysts and diplomats suspected the attack was linked to Uighur sympathisers angered by Thailand’s deportation of more than 100 Uighurs to China the previous month.

Bangkok is currently playing host to a regional meeting attended by some world and business leaders. Police said they were on high alert.

“I have ordered all police under my supervision in the area around Bangkok to monitor news, investigate and gather intelligence on groups who could come in and cause trouble,” said police Lieutenant General Charnthep Sesawet, acting chief for the capital.

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