There's no shortage of evidence that shows pro-Russian rebels shot down a Malaysian jet in Ukraine last week, U.S. Secretary of State John Kerry said.
Malaysia Airlines Flight 17 fell from the sky in Donetsk on Thursday, killing all 298 people aboard.
There's video of a launcher with one surface-to-air missile missing, imagery showing the firing and intercepted calls with rebels claiming credit for the strike, Kerry said.
"We know from intercepts ... that those are in fact the voices of separatists," he told CNN's State of the Union on Sunday. "And now we have a video showing a launcher moving back through a particular area there out into Russia with at least one missing missile on it."
Kerry accused Russia of backing the separatists.
"This is the moment of truth for Russia. Russia is supporting these separatists. Russia is arming these separatists. Russia is training these separatists. And Russia has not yet done the things necessary in order to try to bring them under control," he said.
British Prime Minister David Cameron didn't mince words either on who was to blame. In an op-ed in The Sunday Times, he called the plane crash and its aftermath "an outrage made in Moscow."
Russian President Vladimir Putin fired back with a video statement posted on the Kremlin's official website early Monday, arguing that his country has been pushing for peace in Ukraine.
"We have repeatedly called on all parties to immediately stop the bloodshed and to sit down at the negotiating table. We can confidently say that if June 28 fighting in eastern Ukraine did not resume, this tragedy most likely would not have happened," he said. "However, no one should have the right to use this tragedy to achieve selfish political objectives. Such events should not divide but unite people."
He stressed that safety must be guaranteed for international experts investigating the crash.
"We must do everything to ensure their work has full and absolute security (and) ensure necessary humanitarian corridors are provided," Putin said.
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The escalating conflict in Ukraine "essentially puts the nation on the brink of civil war," Russian President Vladimir Putin said on Tuesday.
His assessment came during a telephone conversation with his German counterpart, according to the Kremlin, the same day Ukraine's military launched its first, formal military action against pro-Russian militants with troops retaking an airport in the eastern Donetsk region after a reported clash with gunmen.
The military action came a day after a Ukrainian ultimatum expired for protesters to lay down their arms, a move that appeared to signal an escalation in the crisis that has sparked a diplomatic row between Ukraine, its Western allies and Russia.
With pro-Russian militants seizing government and police buildings in as many as 10 towns and cities in eastern Ukraine, acting President Oleksandr Turchynov told Parliament "an anti-terrorist operation" was under way in the region.
The aim of the military operation is to "stop attempts to tear Ukraine to pieces," he told lawmakers.
Witnesses reported hearing gunfire and aircraft that appeared to be coming from the airfield in Kramatorsk, which Turchynov's office said was under the control of Ukrainain special forces late Tuesday.
There were conflicting reports about casualties, with Russian state-run media citing varying casualty claims supplied by militants. According to the reports, there were either two injured or four killed, claims that CNN cannot independently verify.
They've given up their ground before - voluntarily, as a political concession. But that seems to be over.
After the deaths of 25 people in clashes a day earlier, Ukrainian protesters are prepared to stand and fight again Wednesday.
Police want to clear them out of central Kiev. Some of them died trying to stay put Tuesday - using projectiles and burning barricades to keep security forces at bay at Kiev's Maidan, or Independence Square.
It was the deadliest day in the months-long standoff between the government and opposition leaders.
Thousands of demonstrators have packed Independence Square since November, when President Viktor Yanukovych reversed a decision to sign a trade deal with the European Union and instead turned toward Russia.
The unrest intensified after an anti-protest law went into effect. Throngs of demonstrators took to the streets to protest the law.
Police and protesters were among Tuesday's dead. A journalist and a government employee died, too.
More than 240 others were hospitalized, Ukraine's health ministry said.
Overnight, demonstrators stocked up, passing stones hand to hand, filling Molotov cocktails and stoking flaming barricades with wood and tires.
They prepared a makeshift compressed-air cannon to catapult the projectiles into police ranks.
Hundreds of others came out to give moral support to those holding the square and to add their numbers to the throng wanting to keep the opposition movement alive.
Corporate lawyer and iReporter Volodymyr Solohub wasÂ one of them. Whenever police threaten to clear the Maidan he goes there.
Tuesday, he watched as protesters rushed injured people from the front lines to medics.
"Some of them had broken hands, and blood was flowing down their faces," he said Wednesday.
Barrages of stun grenades shattered the air around him through the night.
"When it goes off, the whole area vibrates," he said. But the barricades held, and it made him happy.
When the sun rose Wednesday, smoke was still rising from them into the sky.