Bangkok: Cambodian authorities are investigating Australian filmmaker James Ricketson over his alleged links to the country's now-disbanded opposition party, which has been accused of attempting to overthrow strongman Hun Sen in a purported United States-backed conspiracy.

"It is because of his relations with the opposition party, that's why he got into trouble," Sourng Sopheaktra, one of Ricketson's lawyers, told the Phnom Penh Post.

Initial reports said Ricketson, 69, was arrested after flying a drone over a rally on Phnom Penh's riverfront staged by the opposition Cambodian National Rescue Party in June. He is accused of spying against the government.

The opposition party's leaders have been jailed, are in hiding or have fled the country in a sweeping crackdown on opponents of Hun Sen ahead of elections scheduled for mid-year.