(Changes day from Monday to Friday in paragraph 5)
* Four-way talks end with call for end to Ukraine violence
* On ground, pro-Russian gunmen holding their positions
* Kiev's Maidan says it won't budge
* Obama says talks offer hope that diplomacy can work
* Deal did not mention Russia's annexation of Crimea
By Pavel Polityuk and Thomas Grove
KIEV/SLAVIANSK, Ukraine April 18 Armed pro-Russian separatists were still holding public buildings in eastern Ukraine on Friday, saying they needed more assurances about their security before they comply with an international deal ordering them to disarm.
The agreement, brokered by the United States, Russia, Ukraine and the European Union in Geneva on Thursday offered the best hope to date of defusing a stand-off in Ukraine that has dragged East-West relations to their lowest level since the Cold War.
Enacting the agreement on the ground though will be difficult, because of the deep mistrust between the pro-Russian groups and the Western-backed government in Kiev, which this week flared into violent clashes that killed several people.
The fact any deal was reached at all came as a surprise, and it was not immediately clear what had happened behind the scenes to persuade the Kremlin, which had up to that point shown little sign of compromise, to join calls on the militias to disarm.
In Slaviansk, a city that has become a flashpoint in the crisis after men with Kalashnikovs took control last weekend, leaders of the pro-Russian gunmen were holding a meeting early on Friday inside one of the buildings they seized on how to respond to the Geneva agreement.
On the street, there was little change. In front of the Slaviansk mayor's office, men armed with Kalashnikovs peered over sandbags which had been piled higher overnight. Separatists remained in control of the city's main streets, searching cars at checkpoints around the city.
"Are we going to leave the buildings so that they can come and arrest us? I don't think so," said a man guarding the road to the security office, another building the separatists seized, who identified himself as Alexei.
But he acknowledged that the Geneva talks had changed the situation.
"It turns out Vova doesn't love us as much as we thought." said Alexei, using a diminutive term for Vladimir Putin, the Russian president viewed by many of the separatist militias in eastern Ukraine as their champion and protector.
Putin overturned decades of post-Cold War diplomacy last month by declaring Russia had a right to intervene in neighbouring countries and by annexing Crimea.
Moscow's takeover of the Black Sea region, followed the overthrow of Ukraine's pro-Moscow president Viktor Yanukovich, after months of street protests prompted by his rejection of a trade deal with the EU.
In the capital, Kiev, people on the Maidan, the local name given to Independence Square which was the centre of protests that eventually toppled Yanukovich, said the barricades would not come down until the May 25 presidential election.
"People will not leave the Maidan. The people gave their word to stay until the presidential elections so that nobody will be able to rig the result. Then after the election we'll go of our own accord," said 56-year-old Viktor Palamaryuk from the western town of Chernivtsi.
"Nobody will take down our tents and barricades," said 34-year-old Volodymyr Shevchenko from the southern Kherson region. "If the authorities try to do that by force, thousands and thousands of people will come on to the Maidan and stop them."
The Right Sector, a far-right nationalist group whose violent street tactics in support of the Maidan helped bring down Yanukovich in February, saw the Geneva accord as being directed only at pro-Russian separatists in the east.
"We don't have any illegal weapons and so the call to disarm will not apply to us. We, the vanguard of the Ukrainian revolution, should not be compared to obvious bandits," said Right Sector spokesman Artem Skoropadsky.
President Barack Obama said the meeting in Geneva between Russia and western powers was promising but that the United States and its allies were prepared to impose more sanctions on Russia if the situation fails to improve.
"There is the possibility, the prospect, that diplomacy may de-escalate the situation," Obama told reporters.
"The question now becomes, will in fact they use the influence they've exerted in a disruptive way to restore some order so that Ukrainians can carry out an election and move forward with the decentralization reforms that they've proposed," he said at the White House.
The Geneva agreement required all illegal armed groups to disarm, it demanded an end to the illegal occupation of public buildings, streets and squares, and gave a leading role to overseeing the deal to monitors from the Organisation for Security and Cooperation in Europe.
U.S. Secretary of State John Kerry told reporters in Geneva that if by the end of the weekend there were no signs that pro-Russian groups were pulling back, there would be costs for Moscow, a reference to further EU and U.S. sanctions.
"It will be a test for Russia, if Russia wants really to show willing to have stability in these regions," said Ukrainian Foreign Minister Andriy Deshchytsia.
Moscow has denied any involvement with the unrest in eastern Ukraine and rejects allegations that it has agents running clandestine operations on Ukrainian soil.
The Geneva deal contained no mention of Russia's annexation of Ukraine's Crimea Peninsula.
Asked about the absence of any language in the document condemning Russia's intervention in Crimea, Western diplomats said they remained firm that Russian had acted illegally, and denied they had dropped the issue.
The fact the agreement did not address Crimea could put pressure on Ukraine's interim government from its own supporters who are adamant that everything should be done to bring the peninsula back under Kiev's control.
The United States and European Union have so far imposed visa bans and asset freezes on a small number of Russians, a response that Moscow has openly mocked. However, the Western states say they are now contemplating measures that could hurt Russia's economy more broadly.
But some EU nations at least are reluctant to press ahead with more sanctions, fearing that could provoke Russia further or end up hurting their own economies.
Speaking in Geneva, Kerry also took the opportunity to condemn as "intolerable" suggestions in the eastern city of Donetsk that Jews had been ordered to register with authorities.
Pro-Russian militants control buildings in about 10 towns in eastern Ukraine after launching their uprising on April 6.
Separatists occupying a local government building in the city of Donetsk said they would not leave until supporters of Ukraine's new government quit their camp around the Maidan.
Asked how his group will react to the accord in Geneva, Alexander Zakharchenko, a protest leader inside the Donetsk regional government building, told Reuters by telephone:
"If it means all squares and public buildings, then I guess it should start with the Maidan in Kiev. We'll see what they do there before we make our decision here."
In Luhansk, another city where pro-Russian separatists are occupying public buildings, a militia member called Andrey said his group had no plans to withdraw.
"Everything on the ground is the same as it was yesterday and the day before and the day before that. We're not leaving."
Seeking to reassure its eastern allies, NATO announced it was sending warships to the Baltic, while the United States approved more non-lethal military support for Ukraine.
Speaking on Russian television Putin accused the authorities in Kiev of plunging the country into an "abyss".
Kiev fears he will use any violence as a pretext to launch an invasion of eastern Ukraine by Russian forces.
"Instead of realising that there is something wrong with the Ukrainian government and attempting dialogue, they made more threats of force ... This is another very grave crime by Kiev's current leaders," Putin said in his annual televised question-and-answer session with the Russian public.
"I hope that they are able to realise what a pit, what an abyss the current authorities are in and dragging the country into," said Putin. (Additional reporting by Stephanie Nebehay, Tom Miles, Arshad Mohammed and Catherine Koppel in Geneva, and Alexei Anishchuk in Moscow; Writing by Christian Lowe and Richard Balmforth; Editing by Anna Willard)