Mr. Thaksin arrived in the Cambodian capital, Phnom Penh, Tuesday on a private plane. Later this week he is to address economists in his role as an economic advisor to the Cambodian government.

A Cambodian government spokesman welcomed Mr. Thaksin, saying he would provide advice on economic development. But the spokesman warned Mr. Thaksin against using the Cambodian territory for political purposes.

The appointment of Mr. Thaksin as an advisor has heightened tensions between Cambodia and Thailand. Bangkok seeks his return to serve a two-year jail term for a corruption conviction. Mr. Thaksin fled Thailand last year after his trial.

Thai government spokesman Panitan Wattanayagorn says the government will request Mr. Thaksin's extradition through the Foreign Ministry and attorney general's office.

"We'll try our best to communicate with the Cambodia that we are required to seek Khun (Mr.) Thaksin's return to the justice process in Thailand. It's a law that requires us to do so and we also have a treaty with Cambodia to be honored so we do that accordingly."

Relations between the two governments, already tense, worsened in last month after Cambodian Prime Minister Hun Sen invited Mr. Thaksin to Phnom Penh. The Thai government this week revoked an agreement on a maritime boundary and is reviewing other dealings with Phnom Penh. The two countries have recalled their ambassadors.

In the past year, ties have been strained over disputed land surrounding an 11th century Khmer temple just on the Cambodian side of the border. Brief army clashes have resulted in casualties on both sides.

Thai media reported Tuesday that Mr. Thaksin also could face new legal action after giving an interview to a British newspaper in which he spoke frankly over the future of the highly revered Thai monarchy.

Discussion of the monarchy is highly sensitive, and tough laws aim at protecting the institution from outside criticism.

Mr. Thaksin was ousted in a military coup in 2006. He remains very popular among Thailand's farming communities and the urban poor, but the country's middle class, especially in Bangkok, consider him to be corrupt and authoritarian.