Thailand's opposition protesters are preparing to relaunch their campaign to overthrow a government whose prime minister they say is being infuenced by her brother, who was ousted in a coup.

The two-day hiatus in demonstrations in the capital Bangkok was prompted by birthday celebrations for the country's revered king, Bhumibol Adulyadej.

But the protesters have vowed to step up their rallies after the lull in tensions despite a call by the ailing monarch for "stability and security" in his birthday speech.

Akanat Promphan, a spokesman for the demonstrators, said the protesters had no immediate plans for action on Friday and would await an "important speech" in the evening from Suthep Thaugsuban, their leader, about their next move.

The violence - between opposition supporters and security forces - has so far killed five people and left more than 200 injured.

Prime Minister Yingluck Shinawatri is accused by the protesters of running the government under the influence of her brother Thaksin, who was ousted as prime minister seven years ago and is living in exile.

The kingdom remains on edge following several days of street clashes between police using tear gas, water cannon and rubber bullets against rock-throwing demonstrators.

Trips cancelled

With fresh unrest looming, Yingluck has cancelled two planned trips overseas next week to Russia and to the opening ceremony of the Southeast Asian Games in Myanmar, her office said.

The protesters, a mix of royalists, middle class and other Thaksin opponents - sometimes numbering in their tens of thousands - want to suspend the country's democracy in favour of an unelected government run by the "people's council".

Suthep, a former deputy premier who now faces an arrest warrant for insurrection, has pledged to rid Thailand of what he calls the "Thaksin regime".

Demonstrators and police in Bangkok have observed a temporary truce since Wednesday for the 86th birthday of King Bhumibol Adulyadej, who is treated as a near-deity by many Thais.

Any political action or violence during the public holiday would have been seen as a serious sign of disrespect.

The government on Tuesday abruptly ordered police to avoid confrontation with protesters, briefly allowing them into the police and government headquarters in a surprise move that sharply reduced tensions in the capital.