PHNOM PENH—Ousted Thai premier Thaksin Shinawatra arrived in Cambodia to start work as a government economic adviser Tuesday, fuelling tensions between the two countries after a series of border clashes.

Thailand vowed to seek the extradition of the fugitive billionaire, who was ousted in a bloodless coup in 2006 and is living abroad to avoid corruption charges, but Cambodia said it would refuse any request.

The row has plunged relations between the neighboring nations to their lowest for years and threatens to cloud weekend talks between Southeast Asian leaders and US President Barack Obama.

Thaksin landed in a private jet at Phnom Penh International Airport and was escorted into the capital by a convoy of cars under tight security early Tuesday, said an AFP photographer.

"Thaksin is here for the economy and no activities related to politics. It is an honor for Cambodia's economic sector and we hope that Cambodians nationwide welcome him warmly," Cambodian cabinet spokesman Phay Siphan said.

Thaksin is expected to stay a few days and is due to address 300 Cambodian economics experts in Phnom Penh on Thursday as part of his new post.

State TV on Tuesday evening showed Thaksin and Prime Minister Hun Sen embracing, reporting 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 for the new role. Thaksin also planned to visit Cambodia's famed Angkor Wat temple during his trip, television said.

The men were shown laughing and chatting at a house specially prepared for Thaksin, but the exiled leader said on his official Twitter account that he was "really homesick".

"Tonight I will dine with Prime Minister Hun Sen and his family. I want to reiterate that nation, religion and monarchy are always in my mind," Thaksin wrote.

Thailand and Cambodia recalled their respective ambassadors last week in the escalating row over Thaksin, a telecommunications tycoon and the former owner of Manchester City Football Club.

He won two elections and remains a massively influential figure in Thai politics, stirring up mass protests by so-called "Red Shirt" supporters against the government.

His presence on Thailand's doorstep is the closest he has come since he last left the kingdom in August 2008, a move that is likely to alarm the shaky government of Thai Prime Minister Abhisit Vejjajiva.

Tensions between Thailand and Cambodia remain high following recent deadly skirmishes on their disputed border near Cambodia's 11th-century Preah Vihear temple, which was granted World Heritage status in July 2008 by United Nations Educational, Scientific and Cultural Organization (UNESCO).

Abhisit said Thailand would review its extradition treaty with Cambodia if it failed to comply with Bangkok's request.

The Thai foreign ministry said that it was sending the extradition request to the embassy in Phnom Penh late Tuesday and expected to hand the documents to Cambodian officials on Wednesday.

Thailand's cabinet also agreed to cancel an oil and gas exploration deal with Cambodia that was signed during Thaksin's time in power.

Cambodian foreign ministry spokesman Koy Kuong rejected the extradition threat.

"We will not extradite him. We already clarified this case because he is a political victim," Koy Kuong said.

Thailand stepped up pressure on Thaksin Monday, accusing him of "violating" the country's revered monarchy after he was quoted in an interview as calling for the reform of royal institutions.

The country's royalist "Yellow Shirt" group, which helped bring down Thaksin in 2006 and blockaded Bangkok's airports to oust his allies last year, said it would stage a mass anti-Thaksin protest in Bangkok on Sunday.

The visit comes just days before Abhisit is due to chair a summit in Singapore between Obama and leaders of the Association of Southeast Asian Nations (ASEAN), also Sunday.

Singapore Foreign Minister George Yeo said the Thai-Cambodia row worried ASEAN members.

"We are very concerned about this bilateral problem between two fraternal members of ASEAN and we hope they will find a way to reconcile and to act with restraint," Yeo said.