PHNOM PENH, CAMBODIA — At a luxury guesthouse, Cambodia's newest government adviser picks up a copy of his latest book, "Tackling Poverty." It explores how lessons from Thailand can be applied to other developing countries.

"I help tackle poverty worldwide, wherever they need me. Why not my neighbor?" asks Thaksin Shinawatra, the author.

But Mr. Thaksin, a Thai prime minister ousted by a coup in 2006, is no ordinary consultant - and he knows it. The politician's electoral successes antagonized Bangkok's royalist elite. Now, exiled in Dubai and wanted at home on a corruption-related conviction, Thaksin remains a political player who courts controversy.

His recent appointment as an adviser here has injected a new and potentially destabilizing element spilling beyond his home country. A five-day visit earlier this month to Cambodia, which shares a border and centuries of rivalry with Thailand, provoked a nationalist uproar in Bangkok. Both countries withdrew their ambassadors. Thailand tore up a maritime treaty and threatened to seal the border, where rival armies already face off over a disputed Hindu temple. Cambodia later expelled a diplomat for spying.

So far, the diplomatic tensions haven't spilled over to the temple site. The area is one of several poorly demarcated borders that Thailand shares with its neighbors and where sovereignty claims have flared into armed clashes, though rarely for long.

In Cambodia the border also evokes memories of Thailand's arming of the murderous Khmer Rouge during a civil war that Cambodian Prime Minister Hun Sen fought mostly on the opposite side. He has argued that Thailand has no right to demand Thaksin's extradition because it used to shelter senior Khmer Rouge leaders.

Thailand and Cambodia belong to the Association of Southeast Asian Nations (ASEAN). But the Thai government has resisted mediation by the 10-nation bloc.

That leaves the two neighbors at loggerheads over Thaksin. A court in Bangkok is expected to rule next month on the confiscation of more than $2 billion of his frozen money. The case is separate from his 2008 conviction and two-year jail term. But Prime Minsiter Hun Sen has offered Thaksin sanctuary and rejected Thailand's request for extradition.

Feted in Cambodia
Arriving by private jet, Thaksin was given a lavish reception at Hun Sen's heavily guarded compound outside the Cambodian capital. On Nov. 12, he gave a talk to 300 civil servants on economic policy that was broadcast on state television.

Some analysts say the sight of Hun Sen embracing Thaksin as an "eternal friend" plays into the hands of critics who label him a traitorous opportunist. Thai Prime Minister Abhisit Vejjajiva has tried to capitalize on this nationalist anger by talking tough against Cambodia.

"One of the only ways to unite this incredibly divided country is to give them a common enemy," says a Bangkok-based diplomat.

But the row is unlikely to sway Thaksin's large base of supporters, who see him as a political victim. By popping up in Cambodia, which borders Thailand's pro-Thaksin northeast, he has given them fresh hope that he will return.

In an interview, Thaksin says his critics have a "Cold war mindset" toward Cambodia, a smaller neighbor, and argues that economic success there will eventually benefit Thailand. He claims not to be worried by the Thai government's efforts to bring him home.

"It's clear it's [the conviction] politically motivated. The more you try to extradite me, the more you will make the justice system look ugly," he says.

From Dubai, Thaksin travels regularly as a private businessman to Africa and the Pacific. After Mr. Abhisit revoked his Thai passport, he switched to Nicaraguan and Montenegro ones.

But visiting Cambodia with the backing of its leader is far more provocative, given the proximity and tensions between the countries. It also flies in the face of ASEAN's long-held principle that members don't interfere in one another's domestic politics.

Thaksin says that he also made an unannounced visit to Thailand's southern neighbor Malaysia earlier this year, though he didn't meet the prime minister. Thai media has reported previous trips to Cambodia, which Thaksin denies making.

At times, though, his bravado seems tempered by concerns of a backlash among Thais. Asked if Cambodia would become a new base of operations, he shook his head.

"If I were to come back, I would come back quietly and not so often. I don't want the Thai government to be so nervous," he says.

Why Cambodia wants him
To Hun Sen, this nervousness may spell opportunity, says Nidhi Eoseewong, a retired Thai historian. While Thaksin wants to stay in the limelight, Hun Sen is turning Thailand's deep political divisions to his advantage.

Hun Sen "wants to prolong the weakness in Thailand. He's very smart," Mr. Nidhi says.

However, a Cambodian observer, who requested anonymity, says that Hun Sen is driven primarily by frustration over Thai obstruction of Cambodia's plans for the border temple, Preah Vihear. He may have concluded that no favorable resolution is possible with Mr. Abhisit's government, unless international mediators are involved.

For his part, Thaksin describes his alliance with Cambodia's strongman in plainer terms. "I'm unemployed. He's my friend," he says.