Ukraine's military on Friday called on President Viktor Yanukovych to take "urgent steps" to ease turmoil in the country, weighing in for the first time on the ex-Soviet nation's worst crisis since independence.
The army's call on the embattled leader, who on Thursday took indefinite sick leave, came as protesters refused to leave occupied municipal buildings in Kiev and as the West prepared to receive opposition leaders at the weekend.
It also came as a prominent opposition activist who went missing more than a week ago re-appeared bloodied and disfigured, saying he was tortured by unidentified assailants before being dumped in a forest in the freezing cold.
The Ukrainian army has previously said it would not interfere in the protests, which erupted in November after Yanukovych scrapped an integration deal with the European Union in favour of closer ties with Kiev's historical master Moscow.
The unrest has since spiralled into an uprising demanding the president's removal.
The defence ministry said in a statement the seizure of government buildings was unacceptable and warned that "further escalation of the confrontation threatens the country's territorial integrity."
"Servicemen and employees of Ukraine's armed forces... have called on the commander-in-chief to take urgent steps within the limits of existing legislation with a view to stabilising the situation in the country and reaching consent in society," it said.
The outcome of the crisis will likely determine whether Ukraine will revert to close ties with Moscow or move toward closer integration with the West and the two sides have traded accusations of trying to influence Kiev since the protests started.
Ukrainian opposition leaders including boxer-turned-politician Vitali Klitschko on Saturday were due to meet US Secretary of State John Kerry for the first time, a meeting sure to infuriate Moscow, which has repeatedly warned against foreign interference in its former satellite.
The announcement of the meeting, on the sidelines of a security conference in Munich, came as the White House said it was consulting with Congress over possible sanctions on Ukraine.
Opposition leader Arseniy Yatsenyuk of the main opposition Batkivshchyna party, was also due to meet Germany's President Joachim Gauck and Foreign Minister Frank-Walter Steinmeier, along with EU foreign affairs chief Catherine Ashton.
'It is a circus'
The meetings are likely to elicit fury from the Kremlin following warnings by President Vladimir Putin against foreign interference in the ex-Soviet country's worst crisis since its 1991 independence.
Russia's outspoken Deputy Prime Minister Dmitry Rogozin tweeted on Friday that Kerry's planned meetings, which are also expected to include Ukraine's pro-opposition pop star Ruslana, were a "circus."
The announcement of the Kerry meeting came hours after Yanukovych savaged the "irresponsible" opposition for inflaming tensions.
Opposition supporters are refusing to leave their protest camp on Kiev's central square despite a string of concessions from the authorities, including a promised amnesty for jailed demonstrators and Yanukovych's acceptance of his prime minister's resignation.
The protest movement's leaders claim that abuse and beatings of activists are widespread.
Prominent Ukrainian opposition activist Dmytro Bulatov, who went missing more than a week ago, reappeared Thursday night, saying he was blindfolded and tortured by abductors who cut off his ear and drove nails through his hands before dumping him in a forest.
"My hands... they crucified me, nailed me, cut my ear off, cut my face," Bulatov told Channel 5 television, his face swollen and covered in caked blood. "Thank God I am alive."
Defiance and contrition
On Thursday, Yanukovych issued a defiant statement accusing the opposition of behaving irresponsibly.
"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.
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 yielded some ground to the protesters by accepting the resignations of Prime Minister Mykola Azarov as well as allowing the annulment of tough anti-protest laws.
Thousands of demonstrators camp out in much of Kiev's city centre, including radical activists in balaclavas who are patrolling the barricades with crowbars.
A recent outbreak of violence saw several people shot dead and turned parts of the capital into a battlefield.
According to prosecutors, four people have died and 234 people have been arrested across the country 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 $15 billion bailout from Moscow, although Putin this week warned that further payments will not be released until a new government is named.