US Vice President Joe Biden waves after landing at the Boryspil airport in Kiev on April 21, 21014
US Vice President Joe Biden touched down at Kiev airport on Monday for a two-day visit seen as a show of support for crisis-hit Ukraine's pro-Western leaders.
Biden's arrival came as Moscow accused Kiev of violating an international accord aimed at defusing a separatist uprising in Ukraine's pro-Russian east.
On arrival, the US vice president was taken to a briefing with US embassy staff. On Tuesday he was to meet the country's interim president, Oleksandr Turchynov, Prime Minister Arseniy Yatsenyuk and lawmakers.
A senior administration official told reporters travelling with Biden that the vice president would be discussing security, politics, economy and energy issues with the Ukrainian leaders.
The stress would be on maintaining Ukrainian "national unity" and calling for "urgent implementation" of an accord hammered out Thursday in Geneva between Ukraine, Russia, the US and the EU, the official said on condition of anonymity.
That accord, which demands the disarmament of "illegal armed groups" and the end of occupation of public buildings in Ukraine, is largely stalled following the refusal of pro-Kremlin rebels to comply with it.
A deadly attack on a separatist road block near the flashpoint town of Slavyansk on Sunday also ended a brief Easter truce.
At least two rebels were killed in the assault, which Moscow blames on far-right nationalists that helped oust Ukraine's pro-Kremlin president Viktor Yanukovych in February after months of increasingly bloody street demonstrations.
The White House official said the details of the Sunday attack were "still very murky" because international monitors deployed in Ukraine to verify the Geneva accord were barred access to the scene.
The official reiterated US President Barack Obama's warning that Russia - which Washington sees as pulling the strings in the separatist insurgency - would soon feel the "costs" of its actions in Ukraine.
"This is going to be a situation where we take stock and determine in the relatively near term what our next step should be," the official said.
Russian Foreign Minister Sergei Lavrov accused Kiev of reneging on the Geneva accord.
But Ukraine's government said it was taking steps to meet the pact's terms, notably by promising to protect the Russian language across Ukraine and to start a process of decentralising power - two of Moscow's key concerns.