Kiev - US Secretary of State John Kerry will meet Ukrainian opposition leaders for the first time on Saturday in a major show of support for pro-democracy protesters locked in a deadly two-month stand-off with President Viktor Yanukovych.
Among those slated to hold talks with the top US diplomat on the sidelines of the Munich Security Conference are former boxing champion Vitali Klitschko, who leads the UDAR (Punch) party, and opposition politician Arseniy Yatsenyuk.
The announcement from senior US officials came hours after Yanukovych savaged the "irresponsible" opposition for inflaming tensions after he unexpectedly went on sick leave with no end in sight to the turmoil.
The street rallies first erupted when the president backed out of a key pact with the European Union in November in favour of closer ties with Moscow. The unrest has since spiralled into an uprising seeking the president's removal.
The opposition has refused to abandon the protests despite a string of concessions from the government, including a promised amnesty for jailed demonstrators.
Kerry kept up pressure on Yanukovych by holding a conference call with top opposition leaders, while the US administration said it was consulting with Congress about possible sanctions on Ukraine.
"We've been cautiously optimistic that this dialogue between the government and the opposition is beginning to bear fruit", a senior state department official said.
"There's the question of whether they can move on to form a government of national unity. So they're coming to Munich in the middle of this negotiating process on what the political compact might look like going forward."
The official spoke just before Kerry's plane left Andrews Air Force Base en route first for Berlin as part of a three-day trip to Germany.
Representatives of the Ukrainian government were also expected to attend the Munich talks, including foreign minister Leonid Kozhara.
President Yanukovych's sick leave for an acute respiratory infection came after a fraught parliament session on Wednesday night, where he had to personally intervene to prevent a possibly decisive schism in his ruling Regions Party over the amnesty bill.
Hours after the sick leave was announced, Yanukovych issued a defiant statement accusing the opposition of behaving irresponsibly by not calling off the protests.
"The opposition is continuing to inflame the situation and is calling on people to stand in the freezing cold due to the political ambitions of several leaders", he said in a statement on the presidential website.
But in a rare show of contrition, Yanukovych also admitted he needed to take more account of the country's mood.
"From my side, I will show more understanding for the demands and ambitions of people, taking into account the mistakes that authorities always make."
Yanukovych has already yielded some ground to the protesters by accepting the resignations of Prime Minister Mykola Azarov and the entire cabinet, as well as allowing the annulment of tough anti-protest laws.
In his conference call with the opposition leaders, Kerry "underscored the United State's unwavering support for the democratic European aspirations of the Ukrainian people and commended these opposition leaders for speaking out against violence", state department spokesperson Jen Psaki said.
"We're willing to consider sanctions. No decision has been made", she added, after Washington revoked the US visas of several unidentified Ukrainians implicated in violence against the protestors.
Thousands of protesters remain camped out in much of Kiev's city centre, including radical activists in balaclavas who are patrolling the barricades with crowbars.
Clashes between protesters and security forces last week left three activists shot dead and turned parts of the capital into a battlefield, in the country's worst unrest since its independence in 1991.
According to prosecutors, four people have died and 234 people have been arrested across Ukraine in the protests. The amnesty would apply to all those detained save those accused of grave crimes.
Ukraine remains mired in deep economic trouble and has accepted a $15bn bailout from Moscow, though Russia this week warned that further payments will only be released when a new government is named.