The US secretary of state, John Kerry, has said that the US and Europe stand with the people of Ukraine as fears that the Ukrainian army could be deployed against anti-government protesters grow.

Speaking in Munich, Kerry said: "Nowhere is the fight for a democratic, European future more important today than in Ukraine," Kerry told political, diplomatic and military leaders at a Munich security conference. The United States and EU stand with the people of Ukraine in that fight."

Leaders of the opposition were due to meet Kerry in Munich, hours after the Ukrainian army called on the president, Viktor Yanukovych, to act to end the crisis. Moscow also warned Yanukovych that he would lose power if he failed to "quash the rebellion".

Opposition supporters have refused to leave their protest camp in Kiev's Independence Square despite a string of concessions from the authorities, including the resignation of the prime minister, Mykola Azarov.

Several people were shot dead in a recent outbreak of violence in the capital, parts of which have been turned into a battle zone. Opposition activist Dmytro Bulatov, who went missing more than a week ago, reappeared on Thursday night and said he had been tortured by abductors who cut off his ear and drove nails through his hands before dumping him in a forest.

Arseniy Yatsenyuk of the opposition party Batkivshchyna said it was very likely the military would use force against protesters.

His warning came after the defence ministry, which had previously said it would not interfere, said the seizure of public buildings was unacceptable and warned that "further escalation of the confrontation threatens the country's territorial integrity".

Nato's chief, Anders Fogh Rasmussen, said he was "very concerned by attempts to involve the military in the crisis".

Yanukovych on Friday scrapped controversial anti-protest laws that had radicalised the protest movement and signed an amnesty bill for jailed opposition activists, but this will only take effect if protesters vacate the public buildings they have occupied within 15 days.

Germany urged Yanukovych, who has been on sick leave since Thursday, to find a political solution to avoid further confrontation.

"If the fuse on the powder keg is already lit then it is highly dangerous to play for time," the German foreign minister, Frank-Walter Steinmeier, said in Munich.

"That's why we have to tell President Yanukovych and his people to quickly and fully meet the commitments he has made to the opposition."