Mr Thaksin (r) and Cambodian PM Hun Sen play golf together
Cambodia has rejected an extradition request from Thailand for former Thai Prime Minister Thaksin Shinawatra, further escalating a diplomatic row.
Mr Thaksin arrived in Cambodia on Tuesday, after being invited to work as an adviser to the government there.
Thai diplomats gave the extradition papers to Cambodia early on Wednesday.
But Cambodia replied saying it would not consider the request, because it viewed the charges Mr Thaksin faces in Thailand as politically motivated.
Mr Thaksin has been sentenced to two years in jail in absentia by a Thai court, as result of a conflict of interest case.
According to the BBC correspondent in Bangkok, Rachel Harvey, the former prime minister's presence just across the border from Thailand is a source of profound irritation and potential concern for the current government.
Mr Thaksin served as Thailand's prime minister from 2001 to 2006, when he was ousted by a military coup after being accused of corruption and showing disrespect to the country's widely-revered monarch, King Bhumibol Adulyadej.
He has been living in self-imposed exile ever since - mostly in Dubai - but has rarely been out of the headlines, giving a series of high-profile interviews and continuing to make contact with his supporters inside the country.
Rachel Harvey, BBC News, Bangkok
If there is one thing that supporters and opponents of Thaksin Shinawatra can surely agree on, it is this - the fugitive former prime minister of Thailand has a knack for grabbing headlines.
In his latest move, the former premier has taken up a new position as economic adviser to the Cambodian government.
There could be a personal edge to it - Mr Thaksin and Mr Hun Sen are good friends and golf partners.
But the timing was widely interpreted in Thai media as being designed to undermine Thai PM Abhisit Vejjajiva.
Analysts say his visit to Cambodia, and his position as a government adviser there, is bound to stoke tensions in Thailand.
Three Thai diplomats presented papers to Cambodia's foreign ministry early on Wednesday asking for Mr Thaksin's extradition.
It came as little surprise to analysts when the Thai foreign ministry quickly received a reply rejecting the request.
Cambodia's foreign ministry said the legal case against Mr Thaksin was politically motivated, and therefore not covered by the two countries' extradition treaty.
It said he had been toppled from power by the military after being "overwhelmingly and democratically elected by the Thai people".
"We are now considering what next step to take," a Thai foreign ministry spokeswoman told the BBC.
But she made clear that at this stage, the focus was still on pursuing legal avenues that could eventually lead to Mr Thaksin's extradition, rather than further retaliatory measures.
Relations between Thailand and Cambodia are already strained.
Having already withdrawn its ambassador from Cambodia, the Thai cabinet has now decided to scrap joint plans for trade and oil exploration.
There have also been series of disputes centred around the 11th-Century Preah Vihear temple complex near the two countries' border.
The temple was awarded to Cambodia by the World Court in 1962, but has been a flashpoint for tensions since it was granted Unesco World Heritage Status in 2008.
Indonesia's Foreign Minister Marty Natalegawa has expressed the region's concern at the deteriorating relations between Thailand and Cambodia, both of which are members of the supposedly fraternal Association of South East Asian Nations.
"This spat, this division has to end, and we must return to the usual path which is friendship within Asean," Mr Natalegawa told reporters.
The timing of this current spat is particularly embarrassing for the Thais, as Thai Prime Minister Abhisit Vejjajiva is due to chair a meeting between Asean leaders and US President Barack Obama on Sunday, on the sidelines of the Asia-Pacific Economic Cooperation (Apec) summit in Singapore.
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