Addressing reporters at a news conference in Brussels, Ukranian Prime Minister Arseniy Yatsenyuk said, "Russian boots and Russian tanks on the ground [in Crimea] is unacceptable in the 21st century," the Guardian reported in a blog.
European Union ministers were meeting in Brussels to discuss a response to the crisis in Ukraine where lawmakers in the autonomous Crimea region called for a March 16 referendum on whether the peninsula should secede or remain part of the Ukraine.
"This is an illegitimate decision," Yatseniuk said of the move by the Crimean Parliament to conduct a March 16 referendum on whether the autonomous region secedes or remains with Ukraine. "This so-called referendum has no legal grounds at all ... Crimea was, is, and will be an integral part of Ukraine."
Kerry, who met Thursday in Rome with Russian Foreign Minister Sergey Lavrov, blamed Russia for the Crimean move, Politico reported.
"The choices that Russia has made escalated this situation and we believe that Russia has the opportunity now, together with the rest of us, to make the right choices in order to de-escalate," Kerry said.
"Crimea is part of Ukraine. Crimea is Ukraine."
The Guardian also reported Russia pledged to simplify the system under which native Russian-speakers living in a former Russian or Soviet Union territory can obtain Russian citizenship.
During his news conference, Yatsenyuk said he hoped the situation in the pro-Russia autonomous Crimea could be resolved peacefully, but "we are ready to protect our country."
Yatsenyuk thanked the European Union for its help, and called on Russia to back off.
"What we ask -- and what we urge -- is we urge the Russian government to pull back its military into barracks, not to support the illegitimate so-called government of Crimea and to start real talks and negotiations for a peaceful solution," Yatsenyuk said.
"We are ready for cooperation but we are not ready to surrender and to be a subordinate of Russia."
Yatsenyuk also stressed his intent to press for a political-and-trade "association agreement" with the European Union, the Wall Street Journal reported. In November, former President Viktor Yanukovych's decision to reject such an agreement triggered protests and his ouster by the Ukrainian Parliament late last month.
EU ministers said they were concerned about signing such an agreement too quickly because such actions could provoke Moscow at a delicate moment. Yatsenyuk didn't say whether his government wants to seal the deal before Ukraine's elections in May.
"We strongly believe that both Ukraine and European Union are ready to sign the Association Agreement and to undertake real steps to stabilize the situation," Yatsenyuk said.
At the EU meeting, French and German leaders said sanctions would be imposed if efforts to bring about direct contact between Russia and Ukraine failed, the Journal said.
"There will be the strongest possible pressure on Russia to start a process of de-escalation, and there is a possible use of sanctions," French President Francois Hollande said in a media availability." But sanctions aren't there to ramp up tensions. Rather, they're there to open up the way to dialogue."
In a rebuke to Russia's statement that Russian-speakers and pro-Russian Ukrainians in Crimea feel threatened by the new government in Kiev, leaders from the Ukrainian Jewish community, which is mainly Russian-speaking, wrote an open letter to Russian President Vladimir Putin that rejected his argument minorities in Ukraine were under threat, the Guardian said.
"The Russian-speaking citizens of Ukraine are not being humiliated or discriminated against. Their civil rights have not been infringed upon," the letter to Putin said, as translated.
"Meanderings about 'forced Ukrainization' and 'bans on the Russian language' that have been so common in Russian media are in the heads of those who invented them. Your certainty about the growth of anti-Semitism in Ukraine, which you expressed at your press conference, also does not correspond to the actual facts."
Ahead of the summit, the European Union has frozen the assets of 18 Ukrainians accused of embezzlement, among them President Viktor Yanukovych, who was ousted last month and fled to Russia, and his son Oleksandr, the Guardian said.
The United States also announced Thursday it would impose sanctions on individuals and entities and delay visas for those either responsible or complicit in the turmoil in Ukraine.