About 2,000 anti-government protesters huddled by braziers in their main tented camp in snowbound Kiev, in defiance of riot police who herded them away from government buildings overnight.
Dozens of riot police removed barricades leading to the presidency, cabinet offices and parliament early on Tuesday.
Protesters regrouped at Independence Square in central Kiev, where they have set up a makeshift tent village, complete with a stage where singers and speakers provide 24-hour entertainment.
The president's standard, a blue flag with a gold trident in the centre, flew outside his office, signalling Viktor Yanukovich was at work - possibly the first time since protests erupted on November 21 over his decision to scrap a trade pact with the European Union in favour of closer ties with Russia.
Demonstrators had feared the arrival of the riot police on Monday heralded a plan to crush the protests, but there was none of the violence seen last week, when dozens of protesters were wounded.
With the crisis weighing on an economy already on the brink of bankruptcy, Yanukovich will hold talks with three former Ukrainian presidents on Tuesday. He was expected to meet EU foreign affairs chief Catherine Ashton on Tuesday or Wednesday.
Ilya Shutov, an ex-miner from the eastern city of Donetsk, said the protesters would stay until Yanukovich left office.
"We were for the EU association agreement because we thought it would force our authorities to be civilised. Their refusal of Europe is a refusal to be civilised," he said.
"Our goal is to get rid of the Soviet-like authorities."
Visiting Moscow, US Deputy Secretary of State Victoria Nuland made a new appeal for calm in Kiev.
She "expressed US deep concern about the situation in Ukraine, and urged Russia to use its influence to press for peace, human dignity and a political solution", the US embassy in Moscow said in a statement.
"The US supports Ukraine's European choice, a non-violent and just political resolution to the current standoff, and a return to economic health with the support of the International Monetary Fund," it said.
But Russia's lower house of parliament was expected to approve a statement rejecting interference in Ukraine by Western politicians, following a visit to the protests last week by Germany's foreign minister.
In Kiev, liberals and nationalists have taken to the streets for demonstrations that have at times drawn hundreds of thousands.
Thousands have also maintained an around-the-clock protest camp in the city centre, blocked roads, besieged government buildings and occupied the capital's city hall.
Hundreds of thousands of people marched on Sunday, the second weekend in a row that such huge crowds have vented fury at a government they accuse of returning the country to Kremlin control.
In a potent symbol, they tore down and smashed the capital's main statue of Vladimir Lenin, founder of the Soviet Union.
A week earlier, baton-wielding police injured scores of people at similar demonstrations. The police have since held back from using force to dislodge the protesters, but gave them five days from last Thursday to leave the streets.
The protesters say they will not go.