Thailand's king has formally appointed the army chief General Prayuth Chan-ocha as head of the nation's new military junta following the recent coup.

Gen Prayuth had warned the palace that violence in Bangkok and other parts of the country was likely to spread and may "jeopardise national security".

Gen Prayuth, who assumed extensive powers over the Southeast Asian nation since seizing power last week, was endorsed as regime leader at a ceremony in Bangkok this morning.

"I gave my oath that I will perform my duty with honesty," the commander-in-chief told reporters afterwards.

"We hope that the problems will be solved soon so we can return to the right democratic system," he added.

The monarchy headed by the revered but ailing King Bhumibol Adulyadej, aged 86, commands great respect among many Thais.

His blessing has traditionally been a key step in legitimising the recurring military takeovers that have taken place in Thailand, which has now seen 19 actual or attempted coups since 1932.

The king, who is yet to make a public statement on the coup, was not believed to have been present at the closed-door ceremony.

Meanwhile, the leader of mass protests against the former Thai government, was freed on bail by a court today, his lawyer said.

Suthep Thaugsuban, who faces charges of insurrection and a separate case for the murder of rival political supporters in 2010, "is now free to go home," said lawyer Bandit Siripan, but added that he is banned from leaving the country.

Mr Suthep had been held since the coup last Thursday by the military, along with scores of other political figures.