The killing of protesters in the Ukrainian capital of Kiev took place "under direct leadership" of the country's ex-president Viktor Yanukovich, the head of Ukraine's security service has said.
He added that unidentified Russians were at Ukraine's security service headquarters during the protests.
Russian troops near the Ukrainian border will return to its permanent bases after completing its military exercises, Russia's Foreign Minister Sergei Lavrov has said, calling for a "de-escalation" of rhetoric.
According to Reuters, Mr Lavrov said that he is expecting answers from NATO on the military alliance's activity in Eastern Europe.
NASA is to suspend the majority of its ongoing activities with Russia over its "violation" of Ukraine's sovereignty, it announced today.
It added that it would continue to work together with Russia on the International Space Station.
In a statement on Facebook, NASA said: "NASA is laser focused on a plan to return human spaceflight launches to American soil, and end our reliance on Russia to get into space.
"This has been a top priority of the Obama Administration’s for the past five years, and had our plan been fully funded, we would have returned American human spaceflight launches – and the jobs they support – back to the United States next year".
It would be "an historic mistake" for Russia to send its forces over Ukraine's eastern border, Nato's secretary general has warned.
Anders Fogh Rasmussen also told ITV News Europe Editor James Mates that the military alliance would do all it could to protect members if they are attacked by Russia.
NATO Sec Gen @andersfoghr Rasmussen confirms to me the alliance will take all steps to defend any member attacked by Russia, including war.
Rasmussen: "Our guarantee to our members is steadfast". But: "we can't continue to disarm while Rus increases its def spending". #NATO
The Russian government has accused Nato of adopting a 'Cold War' stance by suspending all co-operation with Moscow.
Nato made the decision yesterday and has also begun drawing up plans to give extra support to its European partners.
The build-up of Russian troops on Ukraine's eastern border is "incredibly concerning", Nato's top military commander has said.
General Philip Breedlove said Russia now had enough troops to make an incursion into Ukraine and could feasibly "accomplish its objectives" within as little as three to five days.
The military alliance is now working on a package of proposals by April 15th to reinforce its eastern European allies by air, land and sea.
The US House of Representatives has voted overwhelmingly to provide aid to Ukraine, backing a $1 billion loan guarantee for the Kiev government and imposing sanctions over Russia's annexation of Crimea.
The 378-34 vote was in support of a package already approved by the Senate, meaning it will be sent to the White House for President Barack Obama to sign into law.
Foreign Secretary William Hague has said that Nato has "not seen the evidence" of Russian forces pulling back from the Eastern border of Ukraine.
Nato foreign ministers have met in Brussels to discuss the Alliance’s response to Russia’s seizure of Crimea.
Hague also stated that Nato needed to give "reassurance and confidence to Eastern allies," with the UK already promising "fighter planes to the Baltic", among other measures.
Nato's secretary general said he has seen no evidence that Russia is withdrawing its forces from the border with eastern Ukraine as promised.
"Unfortunately, I cannot confirm that Russia is withdrawing its troops," Anders Fogh Rasmussen told reporters today ahead of a meeting of Nato foreign ministers in Brussels. "This is not what we are seeing."
Rasmussen said Russia had undermined the principles on which a Nato-Russia partnership had been built, and that as a result there could be no more "business as usual".
Russia responded by warning Ukraine against integration with the defence alliance.
"(Past attempts) led to a freezing of Russian-Ukrainian political contacts, a headache between Nato and Russia and ... to a division in Ukrainian society," the Russian Foreign Ministry said.