Ukrainian President Petro Poroshenko on Wednesday accused Moscow of crossing a "red line" by signing a decree to ease the process of obtaining Russian citizenship in eastern Ukraine.
Mr Poroshenko called the law an "another important step on the path to our mental independence", saying that "Ukrainian language is a symbol of our people, our state and our nation".
The State Department also urged Russian Federation to uphold its commitments to a peace settlement, and ease back its occupation of Eastern Ukraine.
Shortly after Yanukovych stepped down and fled to Russia, Moscow seized control of Ukraine's Crimean Peninsula and fomented unrest in the Donbas, where it has backed separatist forces in a war that has killed some 13,000 people and continues despite a cease-fire and peace deal known as the Minsk Accords.
Ukraine Foreign Minister Pavlo Klimkin denounced the move on Twitter as a "continuation of aggression and interference in our internal affairs", urging Ukrainians living under occupation not to apply for Russian passports.
'This is an attempt to justify and legitimize Russia's military presence in the occupied part of the Ukrainian Donbass, ' he added.
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Twitter also sees more operating costs as it cleans up its platform to minimise abusive user behavior. He wrote on Twitter that the company does not "treat me well as a Republican".
In the run up to his election, he said he wanted to "renew relations" with eastern Ukraine and start a "powerful information war to end the conflict".
Russian President Vladimir Putin gestures while speaking to the media after his talks with North Korea's leader Kim Jong Un talk in Vladivostok, Russia, Thursday, April 25, 2019.
President-elect Zelensky, a comedian who has played the role of President in a Russian-language drama but until now has had no political experience, often speaks in Russian.
"Ukraine's new leadership can not fail to understand this", he said.
Over a bitter campaign he consistently presented himself as the only candidate who could stand up to Putin.
"No one is going to force these people to take a Russian passport", Nebenzya said. "We are not forcing them to become Russian citizens".