Ukrainian President Petro Poroshenko has called Russia "an aggressor country" that planned "a well-coordinated hybrid war against Ukraine," as he testified in the treason trial of his ousted predecessor.
Meanwhile, the No. 2 official at the U.S. State Department tried to quash speculation that the United States might end up acceding to Russia's annexation of the Crimean Peninsula as part of a larger peace deal.
Moscow seized Crimea in March 2014, just weeks after then-President Viktor Yanukovych fled to Russia as months of protests culminated in violent clashes in Kyiv.
Testifying by video-link on February 21, Poroshenko said that when Yanukovych fled to Russia, Moscow implemented a plan to seize Crimea and instigate separatism in the eastern regions of Dnipropetrovsk, Kharkiv, Luhansk, and Donetsk, as well as the Black Sea port of Odesa.
"Crimea's annexation was part of Russia's hybrid war against Ukraine," Poroshenko said, adding that he traveled to Crimea in late February 2014 and witnessed how the Russian military was annexing the peninsula.
"Tens of thousands of Russian military personnel that were stationed in Sevastopol [a Black Sea port in Crimea], and tens of thousands of Russian military personnel from inner Russia were involved in the operation to seize the Ukrainian territory," Poroshenko told a Kyiv court.
Yanukovych's defense lawyer asked Poroshenko about an agreement on a peaceful solution to the political crisis signed at the time by Yanukovych and the Ukrainian opposition. But the Ukrainian president said he had never seen that document and was not present when the document was signed.
Poroshenko added that he had voted for the transfer of presidential powers from the "missing" Yanukovych to then-parliament speaker Oleksandr Turchynov in February 2014.
"In the face of the unfolding aggression against our country, we had to do something, as Yanukovych was absent, unreachable, his whereabouts were unknown, and we could not just sit and wait and see what was going to happen," he said.
"The challenges our country was facing then were serious and we were responsible for the nation, for Ukraine's future generations," Poroshenko said.
After the defense tried to challenge Poroshenko with questions about the legitimacy of Yanukovych's powers being transferred to Turchynov, the judge stopped the questioning, saying that lawyers' questions were unrelated to the case's essence.
The months of protests that culminated in February 2014 with Yanukovych fleeing resulted in 104 deaths and 2,500 injured, according to Ukrainian prosecutors. Many of those casualties came when riot police fired on protesters as they marched toward the government's main administration buildings.
Yanukovych has denied ordering police to fire on protesters and claims the violence was a "planned operation" to overthrow his government.
In November 2017, Yanukovych testified by video link from the southern Russian city of Rostov-on-Don, where he is believed to spend much of his time.
If he is convicted by the Ukrainian court and Kyiv seeks his extradition, it is uncertain whether Moscow will agree to the request.
Since the fighting erupted in eastern Ukraine in March 2014, more than 10,300 people have been killed and more than 1.6 million have been forced to flee.
'Crimea Is Ukraine'
In his visit to Kyiv, John Sullivan, who is the principal deputy to Secretary of State Rex Tillerson, visited a memorial honoring those killed in the protests.
And in a speech to university students, he sought to emphasize Washington's policies toward Russia and Ukraine.
"Paradoxically, the Russian aggression designed to divide Ukraine, has created great unity of spirit among the Ukrainian people, while deeply damaging Russia's own reputation and standing in Ukraine and on the world stage," he said.
"Given the high stakes, it's important to be clear about U.S. policies toward the conflict: Crimea is Ukraine. The Donbas is Ukraine. We will never accept trading one region of Ukraine for another. We will never make a deal about Ukraine, without Ukraine," he said.
Sullivan repeated Washington's warnings that Ukraine's government was not doing enough to rein in rampant corruption, which was one of the animating factors in the 2014 protests.
"The Ukrainian people expect Ukraine's leaders to answer this call. The American people do too," Sullivan said. "A stable, democratic, and prosperous Ukraine will be less vulnerable to external threats and serve as a beacon to other nations facing Russian aggressions."
"We want you to prove your detractors wrong," he said, "to show that future elections are not an excuse to pause reform, and that Ukraine will not allow itself to be divided by information or divisive rhetoric and that Ukraine will not be tempted by the False choice of stability or liberty. Ukraine can and must have both."