A look at some of the key players in Thailand's escalating political crisis.
Elected to power in 2001, Thaksin Shinawatra, a telecoms tycoon-turned-politician, drew his support from Thailand's rural poor, particularly in the country's north and northeast.
|Even from his self-imposed exile, Thaksin continues to rally his supporters [AFP]
As head of the Thai Rak Thai (Thais Love Thais) party, he was the first Thai prime minister to complete a full term in office and was re-elected in 2005.
Thaksin's support was greatest in the countryside, buoyed by his village welfare, cheap rural loans and job creation schemes.
But critics accused him of corruption, with his ShinCorp telecommunications profiting massively from government contracts and concessions.
Allegations of corruption, as well as accusations that he had insulted the revered monarchy, eventually led to street protests by the yellow-shirted People's Alliance for Democracy (PAD).
The protests paved the way for the military to launch a bloodless coup in September 2006, while Thaksin was out of the country.
Apart from a brief return to Thailand in 2008, Thaksin has based himself in self-imposed exile ever since.
In October 2008, he was sentenced in absentia to two years in jail for breaking conflict-of-interest laws in a government agency's sale of land to his wife.
His estimated $2bn fortune has also been frozen.
A graduate of the UK's elite Eton College and Oxford University, Abhisit Vejjajiva was elected to power by the Thai parliament in December 2008 after a court forced Thaksin's allies from power.
|Protesters say Abhisit came to power
illegally and must resign [AFP]
Abhisit leads the Democrat Party, which was in power before Thaksin's election in 2001.
The party is the biggest in a fragile coalition government that also includes defectors formerly loyal to Thaksin.
Critics say the coalition was created by the army and have accused Abhisit of being a puppet of senior generals.
His fluent English and overseas education have endeared him to the Thai elite and foreign businesses operating in Thailand.
But that background has done nothing to win over rural Thais who formed the backbone of Thaksin's support.
Analysts say his failure to prevent protesters from wrecking a high-profile summit of Asian leaders has weakened his backing from the influential military.
The "Red Shirt" protesters who have taken to the streets in recent days are supporters of Thaksin Shinawatra, the prime minister ousted in a 2006 bloodless coup.
|Red Shirt protesters have brought large
parts of Bangkok to a standstill [AFP]
The group is centred around a body known as The United Front of Democracy Against Dictatorship (UDD), and has the support of several prominent academics and social activists.
The group was formed in 2008, as a counter to the yellow-shirted anti-Thaksin People's Alliance for Democracy (PAD).
The Red Shirts want the current prime minister, Abhisit Vejjajiva, to resign and call elections, saying that his rise to power was illegitimate.
They also accuse members of the Thai elite, particularly the military and judiciary, of undermining democracy.
Like Thaksin, the Red Shirts draw their support from the poorest sections of society, in particular the north and northeast of Thailand.
Formed in late 2005, the yellow-shirted People's Alliance for Democracy (PAD) emerged from a loose coalition of opponents to Thaksin Shinawatra, then prime minister.
|Yellow Shirt protesters say they chose to colour to show loyalty to the king [AFP]
Unlike Thaksin and the Red Shirts, the PAD draws its support from Thailand's Bangkok-based elite.
The group adopted yellow as their trademark, a colour traditionally associated with the monarchy, in what they say is a show of allegiance to Thailand's king.
In 2006, weeks of anti-Thaksin rallies organised by the PAD culminated in a bloodless coup that forced Thaksin from power.
The group largely disappeared from the scene during the subsequent period of military rule, but was re-formed when elections in late 2007 led to Thaksin's allies returning to power.
The PAD's campaign of street protests escalated to a four-month siege of government offices and finally a blockade of Bangkok's two airports that lasted for more than a week, crippling the country's vital tourism industry.
The PAD stood down again after Thaksin's allies lost power in December 2008, and Abhisit Vejjajiva was appointed Thailand's third prime minister in as many months.
But with the recent escalation of Red Shirt protests against Abhisit's government, PAD leaders have said they are considering calling supporters onto the streets once again.
The recent escalation of protests against Abhisit's government has seen the emergence of a shadowy pro-government group, dubbed the "Blue Shirts".
|The pro-government Blue Shirts have
fought with Thaksin supporters [AFP]
The group is believed to be linked to politician Newin Chidchob, the son of the parliamentary speaker.
Newin, a former Thaksin ally, defected in late 2008 in a move that was seen as key to Abhisit's ability to form a coalition government.
The Blue Shirts first appeared on the scene in March, gathering outside Bangkok's Suvarnabhumi airport to protect it from a possible seizure by anti-government Red Shirts.
Blue Shirt gangs were also seen at the beach resort of Pattaya in early April, where they clashed with pro-Thaksin protesters who later derailed the Asian summit.
Having seen 18 coups since 1932 - when Thailand became a constitutional monarchy - the military remains a powerful force in Thai politics.
|Thailand's military remains a powerful
force on the political scene [AFP]
Opposition to the army's dominance peaked in 1992, following a bloody crackdown on street protests against a military-backed government that left at least 52 dead and many still unaccounted for.
A new constitution introduced in 1997 was intended to usher in a new era of Thai politics, free from military involvement.
But that constitution was annulled following the 2006 coup that ousted Thaksin, after which Thailand again came under the rule of a military-backed government.
In the subsequent waves of yellow- and red-shirted protests, the military has seemed unwilling to intervene, failing to stop last year's demonstrations by the PAD, taking no action against protesters blockading Bangkok's airports, and doing little to prevent the storming of the Pattaya summit.
Thailand is a constitutional monarchy and King Bhumibol Adulyadej is highly revered by virtually all sectors of Thai society.
|Thailand's King Bhumipol is said to be
in poor health [GALLO/GETTY]
Since he ascended to the throne in 1946 King Bhumibol has presided over more than 25 prime ministers and 18 constitutions during his rule.
The king is nominally a head of state and does not publicly arbitrate in times of crisis.
But during the 1992 uprising he was seen as playing key role in bringing an end to the violence, appearing on live TV chastising both the military and protest leaders.
Now aged 81, the king is believed to be in poor health. He has made no public comment on the latest protests.