Pro-Russian separatists in Donetsk say they will not leave the government building there, defying the Kiev authorities and threatening a new international deal on Ukraine.
The separatists' spokesman told the BBC that the Kiev government was "illegal", so they would not go until the Kiev government stepped down.
Russia, Ukraine, the EU and US earlier agreed that illegal military groups in Ukraine must leave official buildings.
They reached the deal in Geneva.
Alexander Gnezdilov, spokesman for the self-proclaimed Donetsk People's Republic, said his group would evacuate the government building in the eastern city only when the "illegal" Kiev government vacated parliament and the presidential administration.
A tense standoff continues in eastern Ukraine, where pro-Russian separatists - many of them armed - are occupying official buildings in at least nine cities and towns.
Another protest leader in Donetsk said the separatists would not leave unless pro-European demonstrators in Kiev's Maidan Square packed up their camp first.
US President Barack Obama cautiously welcomed the Geneva deal, but warned that the US and its allies were ready to impose new sanctions on Russia if the situation failed to improve.
On Friday there were reports of some shooting in Serhiyivka, in Donetsk region.
Ukrainian paratroopers opened fire to remove a protesters' roadblock in Serhiyivka, Interfax-Ukraine reported, quoting local sources. The details have not been confirmed.
Russia denies fomenting separatism in eastern and southern Ukraine.Media spotlight on Putin
Russian newspapers devoted their front pages on Friday to President Vladimir Putin's four-hour televised phone-in, rather than the Geneva talks.
"Vladimir Putin: You don't need to worry about a thing" said the front-page headline in Rossiskaya Gazeta, while Kommersant bore the headline: "Putin charts a stubborn line".
Mr Putin was repeatedly applauded by Russians during the live event, in which he demanded firm security guarantees and equal rights for Russian-speakers in Ukraine.
He said he hoped he would not have to use his "right" to send Russian forces into Ukraine.
Moscow is believed to have thousands of troops massed along the border with its neighbour.
Mr Putin was speaking after Wednesday night's clash in Mariupol, eastern Ukraine, in which three separatists were reportedly killed by Ukrainian security forces after hundreds of pro-Russians attacked a military base.US-UK resolve
At the Geneva talks, the sides agreed that illegal military groups in Ukraine must be dissolved, and that those occupying buildings must be disarmed and leave them.
The foreign ministers also agreed that there would be an amnesty for all anti-government protesters.
But speaking in Washington just hours later, President Obama expressed scepticism as to whether Russia would keep its side of the bargain.
"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," he said.
In a telephone call with UK Prime Minister David Cameron, the two leaders agreed that the United States and Europe were prepared to take further measures to impose a new round of sanctions if Russia failed to help restore order.
The UK is to provide an additional £1m ($1.7m; 1.2m euros) to support the expansion of the OSCE special monitoring mission in Ukraine.
UN chief Ban Ki-moon said he was encouraged by the outcome of the talks and that he expected all sides to "show their serious intention" to implement the agreement.
Ukraine has been in crisis since pro-Moscow President Viktor Yanukovych was toppled in February.
Russia then annexed the Crimean peninsula - part of Ukraine but with a Russian-speaking majority - in a move that provoked international outrage.