Opponents of fugitive former Prime Minister Thaksin Shinawatra, riled by his comments about Thailand's monarchy and the warm welcome he received in neighboring Cambodia, rallied Sunday night in the Thai capital.

Police said 15,000-20,000 people were expected at the protest, organized by the ultra-nationalist People's Alliance for Democracy, whose protests in 2006 helped spark a coup ousting Thaksin.

The rally was the latest reminder of the political turbulence that has wracked Thailand since the movement to oust him for alleged corruption and disrespect to the king was launched almost four years ago.

The event was largely peaceful, though Thai media reported that a passing motorcyclist tossed a firecracker near the stage at one point, slightly injuring several people.

Thailand's poor rural majority, which handed Thaksin two landslide election victories, has by and large remained loyal to him, while his opponents, remain steadfast in their belief that he is a threat to the country's esteemed monarchy.

Both sides have taken to the streets in sometimes violent protests.

Cambodia this month named Thaksin an adviser on economic affairs. The appointment, and a subsequent visit by Thaksin, set off a diplomatic row which saw the two countries recall their ambassadors. A Thai court last year sentenced Thaksin in absentia to two years imprisonment on a corruption charge.

Relations were strained further when Cambodia rejected a formal request from Bangkok to arrest Thaksin for extradition.

As the controversy grew, Thaksin also ruffled feathers by giving an interview in which he made remarks that his critics construed as being insulting to Thailand's monarchy.

In an interview published by the Times of London, Thaksin spoke glowingly of the prospects for Crown Prince Vajiralongkorn once he succeeds his father, King Bhumibol Adulyadej. But he criticized the king's close advisers for interfering in politics. Succession is a sensitive issue, particularly as the 81-year-old king, who has been on the throne for 63 years, has been hospitalized with a lung ailment for the past two months.

Sunday night's protesters sang along to folk songs and jazz music composed by the king, waved the national flag, and shouted, "Long Live The King." On stage, in front of a sign reading "Fight for Thailand, Fight For Our King," speakers led the crowd in condemning Thaksin and his followers as "People who sell the country."

"There is no more time for division. As Thais, we have a duty to protect the throne. We are here to defend the country's most respected and beloved institution," said Suriyasai Katasila, a People's Alliance for Democracy leader. "We are here to protest Thaksin's attempt to undermine the monarchy."

Suriyasai also described Cambodia's appointment of Thaksin as an adviser and refusal to extradite him as "an insult to our country, our sovereignty and our honor."

Nationalist passions have been running high on both side of the border for more than a year, after Thailand first backed, then opposed Cambodia's bid to name a famous temple a U.N. World Heritage site. The Preah Vihear temple was awarded to Cambodia by the World Court in 1962, but some land around it remains in dispute.

That territorial dispute has seen both countries deploy troops to the border, leading to several skirmishes that left at least seven soldiers dead.