BANGKOK - Embattled Thai Prime Minister Yingluck Shinawatra returned to the capital, Bangkok, on Wednesday for traditional New Year celebrations in a display of unity alongside military chiefs before a looming showdown with anti-government protesters.

Demonstrators who accuse Yingluck of being the puppet of her self-exiled brother, former premier Thaksin Shinawatra, have vowed to occupy government ministries and other key sites in Bangkok in their bid to scuttle a snap Feb 2 election.

The protests since late November have pitted the brother and sister's political machine with its base among the rural poor in the north against Bangkok's conservative elite.

It has flared into sporadic violence, and army chief General Prayuth Chan-Ocha refused to rule out a coup after wild clashes outside an election registration centre a week ago. Three people have been killed since Thursday.

Yingluck, who is caretaker leader after calling the snap poll in a bid to defuse the crisis, had spent more than a week outside Bangkok shoring up support in the north but returned to the capital early on Wednesday.

She joined Prayuth and other senior military leaders in paying their respects to retired general Prem Tinsulanonda, the president of King Bhumibol Adulyadej's Privy Council. Prayuth's warning last week was a sobering reminder that the military has staged or attempted 18 coups in 81 years.

In a New Year message aired overnight, Thailand's revered King Bhumibol urged peace, prosperity and unity among Thais.

"Everyone's wishes do not seem to be very different, either for their own sake or for the peace of the country," he said.

Wednesday's largely ceremonial duties were a prelude to what are shaping as rougher days ahead for Yingluck, whose Puea Thai Party normally would be expected to win the election.

The demonstrators, led by fiery former deputy premier Suthep Thaugsuban, have vowed to derail the ballot and demand instead an appointed "people's council" before a future vote.

Suthep has vowed to seize ministries and other sites across the capital, although it is not clear when that will start. The main opposition Democrat Party has also declared it will boycott the election.

Thailand's Electoral Commission has offered to act as a mediator between Puea Thai, the Democrats and the protesters. Commissioner Somchai Srisuthiyakorn said the commission would meet senior members of Puea Thai and the Democrats on Thursday, although he said the protesters had rejected a similar offer.

"I believe that something positive will come out of the meeting and the situation will ease up," Thai media quoted Somchai as saying.

While the protests have mainly been in Bangkok, election registration has also been blocked in at least seven provinces in the south, where the protesters and Democrats draw support.

The wider aim of the protesters is to neutralise the power of Thaksin, who they say has manipulated democracy by buying the support of the rural poor with populist policies such as cheap healthcare and subsidies for rice farmers.

Thaksin was overthrown in a 2006 coup and fled into exile two years later to avoid jail for graft charges he said were politically motivated. In November, Puea Thai tried to push through an amnesty bill that would have allowed Thaksin to return a free man, sparking the latest round of protests.