Mystery drones swarmed the skies despite a flight ban in northeast Thailand.

The unmanned aerial vehicles sparked espionage fears as they flew near Thai military sites in Nakhon Ratchasima province, just hours after local officials imposed a 24-hour ban on drones and kites.

Residents said they saw low-flying drones hovering near an irrigation canal, while some were seen allegedly flying towards the local air base.

A local Suchada Singphakdi said: 'More than 10 drones at Sam Yot, near the Save One road, by the irrigation canal. Very clearly visible. Some are low, and some are high.

'They were flying steadily in the Nakhon Ratchasima city area. Without close observation, they might be mistaken for stars or kites with LED lights.'

Nakhon Ratchasima Governor Anuphong Suksomnit had earlier pushed for flight restrictions following reports of drones flying over strategic military positions.

Police also warned residents in northeast Thailand to monitor Russian tourists as claims emerged of the Cambodian army allegedly enlisting foreign agents to operate in the region.

Territorial clashes flared up earlier this year before a brief ceasefire, but started again this month when Cambodian troops are said to have fired on a Thai engineering team building an access road in a disputed border area.

In the most recent battles, at least 21 Thai soldiers and one civilian have been killed.

In Cambodia, the number of military fatalities is believed to be much higher, though regime chiefs have not revealed the actual figure.

Around 600,000 people have been displaced on both sides of the border.

Cambodia's assault has largely been wayward, unguided rockets fired indiscriminately into Thai territory, including an attack on July 24 that killed eight people and injured 13 others. Thailand has used precision drone strikes and fighter jet strikes on military sites.

Former Khmer Rouge henchman and Cambodian dictator Hun Sen - who was a leading figure in the genocide of his own people in the 1970s before assuming power in 1985 and overseeing the murder of thousands of opposition figures and critics - has repeatedly claimed that he wants peace and that Thailand is the aggressor.

Thai officials claim the ongoing border confrontations are a threat to national security, and the areas must be secured.