The Ukrainian government warned on Friday it could take "more concrete actions'' next week if pro-Russian separatists do not end their occupations of public buildings under the terms of an international accord.

 Foreign Minister Andriy Deshchytsia gave no details and Kyiv has threatened to use force before to little effect. The minister also said that, despite demands from the separatists in the east, the government saw no need under its deal with Russia to dismantle the pro-European Maidan camp in Kyiv.

 Asked whether there was a deadline for implementing the agreement on clearing occupied buildings, Deshchytsia told a news conference that he hoped this weekend's Easter holidays might ease tensions and let monitors from Europe's OSCE security body oversee the process. He noted the amnesty offer.

~Earlier Friday militant leader Denis Pushilin said his men were not bound by Thursday's Geneva deal and would only stand down after the Ukrainian government resigns.

 "Slovyansk is now besieged from all sides," lamented Alexander, a local railway worker. "There is the army all around. And we are going to stay here until the very end. Now we are demanding federalization, we want to have a referendum, and we want people to vote themselves and to make their choice with no Russian troops, no one here. But if something starts, we will ask Russia to intervene to help us have a referendum."

 The agreement followed talks between Ukraine, Russia, the United States and the European Union, and called for all government buildings to be evacuated and for the militants to be disarmed.

 However the deal included few concrete measures for ending the crisis, and many Western leaders were skeptical Russia would hold up its end of the bargain.

Obama threatens more sanctions

 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," the president said. "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."

 Analysts say the prospect of more sanctions is already hurting the Russian economy.  Moscow warned this week its economy might show zero percent growth this year due to the crisis.

 But many global companies are lobbying against sanctions, according to Ben Kumar, a analyst at London investment management firm 7IM.

 "You have this globalization now which means that everyone is linked to everyone else," he explained. "Companies like BP - all the major energy companies are so multinational that if you start to threaten to shut down trade links they will kick up a fuss."

 The West is backing threats of sanctions with a show of military force. Canada is sending six fighter planes to the region to help bolster NATO defenses.
 NATO has ruled out military intervention, but says the deployment is aimed at reassuring allies in eastern Europe.

Amnesty

 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.

 "I would like to mention that the government of Ukraine has already prepared a bill on amnesty," he said. "If people who illegally took weapons and captured buildings lay down weapons and release these buildings, we think that these people should be granted amnesty."

 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.

 However, 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.

National dialogue

~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.

 "We have no wish to put our armed troops in Ukraine, on the territory of a friendly state, on the territory where our brothers live. This goes against the core interests of the Russian Federation."

 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.