Tensions remain high in eastern Ukraine after at least three died in a day of shooting during what was supposed to be an Easter truce.
In an exclusive interview with NBC News, the Ukrainian Prime Minister warns of the dangers of unchecked Russian expansion and aggression.
Russia, the US and the EU say that all sides have agreed to steps to "de-escalate" the crisis in Ukraine at talks in Geneva.
US Vice President Joe Biden is set to announce a package of assistance to Ukraine focused on the economy and the energy sector.
Mr Biden has arrived in Kiev for a two-day visit, where he will set out plans to help the Ukrainian government better exploit the country's natural gas resources, along with measures to ensure international aid money is spent efficiently.
Vladimir Putin has signed a decree to rehabilitate ethnic minorities in Crimea who suffered under Soviet dictator Josef Stalin.
Among the groups the decree concerns is Crimea's large Tatar population, which has largely opposed the peninsula's annexation by Russia.
"I have signed a decree to rehabilitate the Crimean Tatar population, the Armenian population, Germans, Greeks - all those who suffered during Stalin's repressions," Mr Putin told a State Council meeting.
Russian foreign minister Sergei Lavrov has accused Ukraine of violating an agreement reached in Geneva last week aimed at averting a wider conflict.
"Steps are being taken - above all by those who seized power in Kiev - not only that do not fulfil, but that crudely violate the Geneva agreement," he said.
Lavrov also told a news conference that a deadly gunfight early on Sunday near a Ukrainian city controlled by pro-Russian separatists showed Kiev did not want to control "extremists".
The Kremlin has approved plans to make it easier for Russian-speaking citizens of former Soviet states to become Russian citizens.
The move, which has been signed off by Vladimir Putin, will affect citizens of countries including Ukraine, Belarus and the Baltic states, along with countries in central Asia.
Russia accused Ukraine of "violating" an Easter truce after at least three people were killed in a gunfight in the early hours of Sunday near a Ukrainian city controlled by pro-Russian separatists.
The separatists said armed men from Ukraine's Right Sector nationalist group had attacked them.
The Right Sector denied any role, saying Russian special forces were behind the clash in Slaviansk.
"The Easter truce has been violated," the Russian foreign ministry said in a statement.
The Russian government has blamed pro-Ukrainians for the shooting of at least two people at a check point in eastern Ukraine. However Kiev claims the attack was staged by pro-Russian separatists to further destablise the country.
The self-styled mayor of the eastern Ukrainian city of Slaviansk, which is controlled by armed pro-Russian separatists, said he had been in contact with mediators from the Organisation for Security and Cooperation in Europe (OSCE).
Vyacheslav Ponomaryov, speaking at a news conference in Slaviansk, did not say what he had discussed with the mediators.
Ukraine's Right Sector nationalists denied playing any role in a gunfight in Slaviansk, eastern Ukraine, in which at least two people were killed. They claimed Russian special forces for being behind the attack.
"It is a blasphemous provocation from Russia: blasphemous because it took place on a holy night for Christians, on Easter night. This was clearly carried out by Russian special forces," Artem Skoropadsky, a spokesman for Right Sector, told Reuters.