BANGKOK (Reuters) - Police in Thailand on Tuesday said they have increased security at major landmarks in the capital Bangkok, at airports and in surrounding provinces following reports of bomb plots just weeks after deadly attacks rocked the country's south.

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

"The deputy prime minister instructed security agencies closely track and monitor anything unusual including things used to prepare bombs and cars," Thawip Netniyom, chief of Thailand's National Security Council, told reporters.

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

Popular tourist destination Thailand 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 between Aug. 11-12 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, which accounts for 10 percent of gross domestic product, has weathered more than a decade of unrest including two military coups and the recent bombings.

Britain's Foreign Office advised travelers to exercise caution following the August bombings.

"You should exercise caution, particularly in public places ... Further incidents are possible in these and other areas of Thailand," the Foreign Office said.

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

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 sympathizers 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 of Provincial Police Region 1, which oversees areas around the capital.

(Reporting by Aukkarapon Niyomyat, Panarat Thepgumpanat and Pracha Hariraksapitak; Writing by Amy Sawitta Lefevre; Editing Michael Perry)