Protesters and Ukrainian police were on Saturday still locked in a tense standoff in Kiev after a night of sporadic clashes that erupted despite a truce.

The epicentre of the two month-long crisis was relatively calm early Saturday but hundreds of protesters were still at the scene with the security forces on the other side of their lines.

Overnight, demonstrators had hurled Molotov cocktails at police who responded with stun grenades and rubber bullets, AFP correspondents said.

The exchanges on Grushevsky Street in Kiev lacked the ferocious intensity of those earlier in the week but will raise concerns about the sustainability of the truce.

The clashes had killed five activists earlier in the week, according to protesters. The authorities have confirmed two shooting deaths but insisted police were not involved.

Demonstrators also set fire again to the barricade of tyres they have made at their frontline, sending black smoke and yellow flames into the night sky. Protesters constantly threw new tyres on the fire to keep the blaze going.

The wind blew the noxious smoke towards the police, leaving the demonstrators almost invisible for the security forces.

However by the morning, the protesters allowed the fires to dwindle almost to nothing and used them mainly to warm themselves on another freezing day in Kiev, where temperatures plumetted to -20 Celsius overnight.

The police and protesters had since Thursday morning largely observed a truce brokered by opposition leader and world boxing champion Vitali Klitschko to give negotiations a chance.

The interior ministry meanwhile said a body of a police officer was found in southern Kiev, though without linking it to the protesters or clashes which have mostly engulfed the city centre.

The ministry further accused the opposition camp's security of "attacking three police officers" near the Independence Square protest hub, injuring one of them with a knife and holding the other two captive.

The opposition denied responsibility for the attack or the killing Friday and asked the police "not to provoke the situation by spreading false and dangerous news."

"The resistance headquarters categorically denies this and consider this a conscious provocation done in order to stoke police outrage against the protesters," said a statement posted on the website of the Batkyvschina (Fatherland) party early Saturday.