Pro-Russian rebels kept their grip on seized government buildings in Ukraine on Friday, a day after Kiev struck a deal with Russia and the West aimed at easing the crisis in the ex-Soviet republic.
As part of the surprise agreement hammered out in talks in Geneva Thursday, "all illegal armed groups" were due to disarm and leave seized state buildings.
But the pro-Kremlin gunmen who have overrun nearly a dozen towns and cities across Ukraine's Russian-speaking southeast showed little sign of leaving.
In Slavyansk, scores of gunmen remained holed up inside a police station and manned a barricade of tyres outside.
Six armoured personnel carriers captured by the gunmen from the Ukrainian army on Wednesday during a failed operation to oust the militantsremained parked on the streets, a humiliating reminder to the pro-Western interim government in Kiev that it was incapable of dislodging them by force.
In the main regional city of Donetsk, militants underlined their defiance by blaring the Russian national anthem.
The actions over the next couple of days in Ukraine's southeast will put to the test the deal struck by Kiev, Moscow, Washington and Brussels that aims to ease the worst East-West crisis since the end of the Cold War.
US President Barack Obama, who has locked horns with Russian President Vladimir Putin over Ukraine's future, reacted cautiously to the agreement.
"We are not going to count on it until we see it," he said, warning that if progress was not evident within days, "additional consequences" would be imposed on Russia on top of sanctions that Washington has already imposed targeting Putin's inner circle.
The Geneva agreement laid out concrete steps to restore security in Ukraine, which was plunged into crisis in late February when months of protests culminated with the overthrow of the country's pro-Kremlin president, leading to Russia's annexation of the Crimean peninsula.
Over the past two weeks, pro-Kremlin separatists have grabbed command of 10 towns in Ukraine's southeast. Kiev and much of the West say elite Russian military units were involved in the occupations, allegations Moscow has denied.
Under the Geneva agreement, the pro-Western protesters who have maintained barricades in central Kiev's Independence Square known as Maidan would also appear to have to end their occupation, which they have vowed to uphold until a presidential election is held May 25.
But they too remained defiant.
"For us, for Ukraine, for the people on Maidan, it means nothing, it is piece of paper. It is an agreement that was signed behind our backs," engineer Valery Levchunets, 46, told AFP on the square.
UN chief Ban Ki-moon hailed the "urgent steps" taken in Geneva, but said the situation "remains extremely volatile" and said he now expected all sides to "show their serious intention" to implement the agreement.
Obama said while "there is the possibility, the prospect, that the diplomacy may de-escalate the situation," he was coordinating with leaders in Europe about further sanctions against Moscow if there were no progress within days.
"We have put in place additional consequences that we can impose on the Russians if we do not see actual improvement of the situation."
The situation in southeastern Ukraine remained volatile.
Overnight Wednesday, three pro-Russian militants were shot dead and 13 were wounded when Ukrainian interior ministry troops they attacked with guns and petrol bombs in the southeastern port city of Mariupol responded with live fire.
Ukraine claims to be holding 10 Russian "spies" it believes were sent to stir up unrest. It has also, according to the Russian airline Aeroflot, banned the entry of Russian males aged 16 to 60.
There was no immediate reaction to the agreement from Putin, who on Thursday warned that Ukraine was plunging into the "abyss."
The Russian leader said he had a "right" to send troops into Ukraine but "very much hoped" that he would not have to do so.
Russia currently has tens of thousands of soldiers massed on Ukraine's eastern border.
Putin has repeatedly denied that Russian special forces are operating in Ukraine's east and blames the turmoil there on Kiev's interim leaders.
In an apparent bid to reassure his counterparts in Geneva, Russian Foreign Minister Sergei Lavrov said Russia had "no desire" to send troops into Ukraine.
The Geneva deal also said that a dialogue should be launched that included all Ukrainians -- addressing Moscow's concerns that the rights of Russian speakers be assured.
Analysts say that the agreement was a face-saving solution for Russia.
"I can see why they (Russians) did this as they felt that the sanctions were quite close to being imposed, so they had to take a step back," Kiev-based political scientist Andreas Umland said.
"But I'm sceptical... I don't think it's all over."
No timeline was given for the implementation of the agreement, but Ukraine's foreign minister said it should begin "in the coming days".
Separately, the European Union announced Thursday it had agreed to hold talks with Russia on its gas supplies to Europe through Ukraine, warning Moscow its reliability as an energy source was at stake.
The announcement came as Putin ramped up pressure on Ukraine's struggling economy by setting a one-month deadline for Kiev to settle its debt for gas imports from Russia.