Pro-Russian militants continued occupying government buildings in eastern Ukraine Friday, after Kyiv and Moscow reached a deal to lower tensions.
Militant leader Denis Pushilin said his men are not bound by the Thursday deal and will only stand down after the Ukrainian government resigns.
The deal followed talks between Ukraine, Russia, the United States and the European Union. It called for all government buildings to be evacuated and for the militants to be disarmed.
But it included few concrete measures for ending the crisis, and many Western leaders were skeptical Russia would hold up its end of the bargain.
U.S. President Barack Obama said Washington will continue preparing sanctions against Russia in case it does not take steps to de-escalate the situation.
"We are coordinating now with our European allies. My hope is that we actually do see follow-through over the next several days but I don't think given past performance that we can count on that. And we have to be prepared to potentially respond to what continue to be efforts of interference by the Russians."
A joint statement from the four powers says amnesty will be granted to protesters who surrender weapons and leave the buildings, except for those found guilty of capital crimes.
Ukrainian Prime Minister Arseniy Yatsenyuk told parliament Friday that he would abide by the amnesty deal.
The seven-paragraph agreement does not specifically require Moscow to withdraw 40,000 troops massed on its border with Ukraine, and does not reference Russia's annexation of Ukraine's Crimean peninsula last month. It also does not obligate Moscow to hold direct talks with the interim government in Kyiv.
But the four-party statement says monitors from the Organization for Security and Cooperation in Europe will immediately begin to put the de-escalation measures into place.
Russian Foreign Minister Sergei Lavrov spoke separately following the Geneva talks, saying the four parties will work to establish a broad national dialogue to ensure protection of Ukrainians' rights.
Moscow has repeatedly insisted it has the right to protect Russian speakers in Ukraine. It accuses the new Ukrainian leadership of being anti-Russian and anti-Semitic, and of threatening the rights of pro-Russians.
Pro-Russian gunmen have seized Ukrainian government buildings in nearly a dozen eastern towns and cities, while Ukrainian troops have launched operations to retake the buildings. It remains unclear how much actual fighting has taken place.