Cambodia has ordered all Thai air traffic control staff to leave work after one of them was arrested on charges of spying on fugitive Thai leader Thaksin Shinawatra, a company letter showed Thursday.

Thai-owned civil aviation company Cambodia Air Traffic Services (CATS), which oversees Cambodian air space, banned the Thai employees after a Cambodian government official was appointed caretaker of the firm.

It was not immediately clear if the ban was temporary or permanent.

"The caretaker has prohibited the Thai expatriates from performing their duties," said company vice-chairman Sirichai Rasameechan in an explanatory letter sent to Thailand's stock exchange, where the company is listed.

The decision deepens a diplomatic crisis between the neighbouring countries over Cambodia's appointment of Thaksin as an economic adviser and its refusal to extradite the ousted prime minister to Bangkok.

Siwarak Chothipong, 31, an employee at CATS, was arrested a week ago on charges of supplying details of Thaksin's flight schedule to his country's embassy when the Thai tycoon visited Phnom Penh last week.

On Tuesday Cambodian officials allowed Thai diplomats to make their first visit to see the detained employee.

Bangkok earlier this month withdrew its ambassador from Cambodia over Thaksin's appointment, a move that Phnom Penh reciprocated.

Cambodia then expelled the first secretary of Thailand's embassy in Phnom Penh last Thursday after alleging that Siwarak had passed information to the diplomat. Thailand reciprocated hours later.

Thaksin was toppled in a coup in 2006 and is living abroad to avoid a two-year jail term for corruption, but he has been stirring up protests in his homeland against the current Thai government for the past year.

Angered by his presence in Cambodia, Thailand last week put all talks and cooperation programmes with Cambodia on hold and tore up an oil and gas exploration deal signed during Thaksin's time in power.

Tensions were already high between the two countries following a series of deadly military clashes over disputed territory near the 11th century Preah Vihear temple on their border.

CATS is a fully owned subsidiary of Bangkok-based Samart corporation, which has a 32-year air traffic control concession. Local media said the company employees nine Thai nationals.