Thousands of protesters have remained in Kiev's main square despite a deal aimed at ending Ukraine's political crisis, in which dozens have died.
The pact, signed on Friday by President Viktor Yanukovych and the opposition, says a unity government will be formed and a presidential election held.
But many protesters do not believe Mr Yanukovych can be trusted.
The US and Russian presidents have agreed that the deal needs to be swiftly implemented, officials say.
Russia's Vladimir Putin told Barack Obama that Russia wants be part of the implementation process in a telephone conversation on Friday, a US State Department spokesperson said.
The deal, reached after mediation by EU foreign ministers, came after the bloodiest day since the unrest began in November.
Police opened fire on Thursday on protesters who have been occupying Independence Square in central Kiev. The health ministry said 77 people had been killed since Tuesday.
The deal has been met with scepticism by some of the thousands of protesters who remain in the square.
Opposition leaders who signed it were booed and called traitors by crowds, the BBC's Gavin Hewitt reports from Kiev.
Earlier, coffins of anti-government protesters were carried across the square as funeral ceremonies for those killed in the clashes got underway.
Meanwhile one group of far-right protesters is threatening to take action if President Yanukovych does n.