PHNOM PENH: Thailand was set to formally ask Cambodia Wednesday to extradite Thaksin Shinawatra, deepening a row over Phnom Penh's appointment of the fugitive former Thai premier as an economic adviser.

Thaksin, who was toppled three years ago in a coup and is living abroad to avoid a jail term for corruption, arrived in Cambodia on Tuesday to take up his new position and was welcomed by Cambodian Prime Minister Hun Sen.

Cambodia has vowed to refuse any request from its larger neighbour for the extradition of the billionaire tycoon, saying that the charges levelled against Thaksin in Thailand were politically motivated.

Tensions are already running high between the two countries following a series of clashes over a temple on their border and the row threatens to mar a weekend summit of Southeast Asian leaders with US President Barack Obama. Related article: Thaksin visit could push Thailand and Cambodia to war: analysts

Thai foreign ministry officials said diplomats would hand the extradition papers to Cambodian authorities early on Wednesday. Thailand and Cambodia recalled their ambassadors from each other's countries last week.

"The papers were conveyed to our embassy in Phnom Penh late Tuesday and we believe they can be submitted to the Cambodia foreign ministry tomorrow," senior Thai Foreign Ministry official Panich Vikitsreth told AFP.

"We believe our request will reach the Cambodian foreign ministry during the period of time that Thaksin stays there."

Thaksin is due to give a speech to 300 Cambodian economics experts on Thursday. Cambodian officials have said he will stay in the country for two or three days but is not intending to live there.

Twice-elected Thaksin fled Thailand in August 2008, a month before a court sentenced him to two years in jail in a conflict of interest case. He had returned to Thailand just months earlier for the first time since the coup.

But he has retained huge influence in Thai politics by stirring up protests against the current government, and analysts said that in his close friend Hun Sen he had found a new way of pushing his campaign for a return to power.

Thailand's government upped the pressure on Thaksin this week by accusing him of offending the revered monarchy after he was quoted by the website of British newspaper The Times as calling for reform of royal institutions.

Defaming the monarchy, led by 81-year-old King Bhumibol Adulyadej, is a crime punishable by up to 15 years in jail in Thailand. The king has been in hospital since September with a lung and chest infection.

In a radio broadcast from Phnom Penh late Tuesday, Thaksin issued an apology to the monarchy but repeated his claim that the newspaper had put a misleading headline on the story.

"I have loyalty. I reaffirm that I will not betray my nation or the monarchy," he said.

He also said that he would visit Cambodia infrequently in his new job as adviser to the government, adding: "I will come when I have to come." Otherwise, he would give advice via email and the Internet, he said.

Cambodian state television late Tuesday showed Thaksin and Hun Sen embracing, reporting that the Cambodian leader pronounced him an "eternal friend" and "the best adviser with economic leadership."

Thaksin reportedly thanked Hun Sen for offering the adviser post and said "nothing can compare" to his excitement over the new role.

Thaksin also planned to visit Cambodia's famed Angkor Wat temple during his trip, television reports said.

Cambodia and Thailand have fought several deadly skirmishes over another ancient monument, the 11th-century Preah Vihear temple, since it was granted UNESCO World Heritage Status in July last year.