The United States says Russia has a "responsibility" to call on pro-Russian militants occupying government buildings in eastern Ukraine to evacuate.
State Department spokeswoman Jen Psaki said Friday that if Russia does not take steps to de-escalate the situation and implement Thursday's deal with Ukraine, aimed at lowering tensions, there will be "consequences."
Militant leader Denis Pushilin said earlier that his men are not bound by the deal and will only stand down after the Ukrainian government resigns.
Psaki said the U.S. rejects those comments and the separatists' claim that the new Ukrainian government took power in a coup.
Thursday's agreement followed talks between Ukraine, Russia, the United States and the European Union. It calls for all government buildings to be evacuated and for the militants to be disarmed.
But it includes few concrete measures for ending the crisis, and many Western leaders are skeptical about Russia holding up its end of the bargain.
Psaki told reporters Friday the U.S. believes Russia has the influence and ability to implement the accord, noting what she described as a "clear and strong connection" between the separatists and Russia. But she said the U.S. is "clear-eyed" about Russia's record of not implementing steps in the past and will test over the coming days whether Russia will follow through this time.
U.S. President Barack Obama said Washington will continue preparing sanctions against Russia in case it does not take the appropriate steps.
"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.