KIEV - US Vice President Joe Biden arrived in Kiev Monday in a show of support for the pro-Western government, as Russia accused Ukraine of reneging on an international accord meant to defuse tensions over its separatist east.
Biden's two-day visit comes with the clock ticking on a White House warning of further sanctions against Moscow if it fails to implement the agreement hammered out last Thursday in Geneva with Ukraine, the United States and the European Union.
Russia has lashed out at claims that it is dragging its feet on implementing the deal, laying the blame squarely on Kiev for violating the agreement.
"The Geneva accord is not only not being fulfilled, but steps are being taken, primarily by those who seized power in Kiev, that are grossly breaching the agreements reached," Russian Foreign Minister Sergei Lavrov said at a Moscow press conference.
The pact has been badly undermined by a deadly weekend shootout in Ukraine's restive east on Sunday, and an obstinate refusal to stand down by pro-Kremlin militants who have seized control of nearly a dozen towns in the region.
The accord calls for all "illegal armed groups" in Ukraine to surrender their weapons and halt the occupation of public buildings and other sites.
Washington has warned Moscow - which it believes is pulling the strings in Ukraine's insurgency - that time is running out for the accord to be put into practice.
The White House said Biden - who has emerged as the Obama administration's top pointman on the crisis - would "consult on the latest developments in east Ukraine" during his trip, which comes amid the worst East-West crisis since the Cold War.
On Monday he was due to speak with US embassy officials in the Ukrainian capital. On Tuesday he was to meet with the country's interim president, Oleksandr Turchynov, Prime Minister Arseniy Yatsenyuk and lawmakers.
The United States and its NATO allies have bolstered military deployments in eastern Europe. Washington and Brussels have also pledged billions to shore up Ukraine's battered economy.
Moscow though has cautioned that it will not tolerate further US sanctions if the deal falls apart, while stressing that it has tens of thousands of troops massed on Ukraine's doorstep.
It says Ukraine's leaders - whom it sees as illegitimate - are using force against the separatist "protesters". It also wants to see anti-Russian demonstrators in Kiev cease their occupation of the capital's main square in line with the Geneva agreement.
A bullish Lavrov said that efforts to cut Moscow off from the international community through sanctions would prove fruitless.
"Attempts to isolate Russia have absolutely no future because isolating Russia from the rest of the world is impossible," he said.
In Ukraine's east, the situation appeared calm Monday, with insurgents still firmly entrenched in public buildings they have occupied for over a week.
"There was no shooting overnight," Yevgen Gorbik, a rebel wearing camouflage and a military cap and standing at a barricade in the flashpoint town of Slavyansk, told AFP.
"We will only shoot if attacked," he added.
Gorbik summed up the bellicose posturing and political jockeying by saying: "Currently, we have a virtual president in Ukraine, a virtual army, and a virtual war." On Sunday, though, the bullets were real in a shootout at a roadblock near the rebel-held town of Slavyansk that killed at least two of the separatist militants.
Pro-Moscow insurgents in Slavyansk and the Kremlin blamed the attack on Pravy Sektor ("Right Sector"), an ultra-nationalist group at the vanguard of Kiev street protests that forced the February ouster of pro-Moscow former president Viktor Yanukovych.
But Ukrainian officials and Pravy Sektor dismissed the allegation as Russian "propaganda". They ridiculed the purported discovery of a business card belonging to the leader of Pravy Sektor in one of the attackers' cars, which Russian media had claimed was proof of the group's involvement.
The self-styled leader of Slavyansk, Vyacheslav Ponomaryov, said a total of three rebels and two attackers had died in the attack, though AFP saw the bodies of only two militants.
Ponomaryov announced a midnight-to-dawn curfew in the town and appealed to Russian President Vladimir Putin to deploy troops to the region as "peacekeepers" - or at least send weapons to help fight the "fascists".
Russia's foreign ministry issued a statement after the gunfight expressing its "outrage" at the violence.
OSCE to triple monitors
A spokesman in Kiev for the Organisation for Security and Cooperation in Europe, which is monitoring implementation of the Geneva agreement, told AFP there was "no confirmation" of the separatists leaving occupied buildings.
Spokesman Michael Bociurkiw said the OSCE planned this week to triple the number of monitors in the country. Currently there are 100, with more than half of them in the east, where they were facing difficulties in travelling through rebel roadblocks.
Putin last week belatedly admitted the Russian military played a role in Crimea, but continues to deny that his army is operating in east Ukraine.
Nevertheless, he asserts he has a "right" to send in forces to his eastern neighbour, which shares historical and linguistic ties with Russia.