The oath-taking allows the government to finally start working on tackling Thailand's economic problems and fostering reconciliation after months of political turmoil that peaked with a blockade of Bangkok's airports last month.

The Oxford-educated Abhisit was elected prime minister by parliament last week following a court verdict on December 2 which disbanded the ruling party loyal to ousted former premier Thaksin Shinawatra.

"I bless you to work for the peace and order of the nation," widely revered King Bhumibol Adulyadej, 81, said in a speech broadcast on national television.

"If you help each other you can give the country peace and order and make the country get through the current situation. That is all Thais want and it can sustain Thais," the king said.

The previous government's collapse came after months of protests by the royalist People's Alliance for Democracy (PAD) who accused it of being a corrupt front for the now-exiled Thaksin and of trying to damage the monarchy.

Thaksin supporters have now pledged to rally in Bangkok on Sunday and threatened to move to parliament on Monday when Democrat Party leader Abhisit's government is due to present its policies to legislators.

The 44-year-old Abhisit said he would heed the king's words. "I will take His Majesty's royal advice to heart. His Majesty wished us to work successfully in order to make the country and the people happy and that is the most important," Abhisit said after the swearing in.

He also said he wanted to "bring back harmony" to Thailand, brushing off opponents' claims that the new government - whose foreign minister openly backed the airport blockade - was undemocratic.

The new Cabinet includes a number of controversial appointments, not least Foreign Minister Kasit Piromya, who was a vocal supporter of the seizure of Suvarnabhumi international airport in late November.

The blockade caused some of the massive economic damage that must now be repaired by the Cabinet, whose economic team is headed by Finance Minister Korn Chatikavanij, an Oxford contemporary of Abhisit and former banker.

The choice of ministers was partly influenced by the need to bring in members of coalition parties that have backed Abhisit, as well as defectors from the former ruling People Power Party which was allied to Thaksin.