Secretary of State John Kerry says the Russian buildup of troops on its border with Ukraine is creating a climate of fear and intimidation in that country.
Kerry spoke after meeting Sunday night in Paris with Russian Foreign Minister Sergey Lavrov and said he told the diplomat that Ukrainians must be allowed to decide their own future.
"The United States is consulting with Ukraine at every step of this process, and we will not accept the path forward if the legitimate government of Ukraine is not at the table,'' Kerry said.
Kerry described his talks with the Russian diplomat as "a frank conversation" about Russia's moves in Crimea and the large gathering of troops along the border with Ukraine.
"I made clear the United States still considers the Russian actions to be illegal and illegitimate,'' Kerry said.
Lavrov called the meeting "very, very constructive.'' But he said Ukraine cannot function as a "unified state" and should be a loose federation of regions choosing their own economy and language.
Lavrov also made his case in a Saturday interview on Russian-controlled TV, saying a federation is the only way to guarantee Ukraine's neutrality.
"We can't see any other way to ensure the stable development of Ukraine but to sign a federal agreement," Lavrov said in the interview. He reiterated Russian claims that the deployment of tens of thousands of troops near the Ukraine border were solely to conduct military exercises.
"We have absolutely no intention of, or interest in, crossing Ukraine's borders," Lavrov said.
U.S. officials have insisted that any changes to Ukraine's governing structure must be acceptable to the Ukrainians. Ukrainian officials are wary of decentralizing power, fearing that pro-Russia regions would hamper its western aspirations and potentially split the country apart. However, they are exploring political reforms that could grant more authority to local governments.
Kerry had been headed home from Saudi Arabia on Saturday when he abruptly headed to Paris after a refueling stop in Shannon, Ireland.
Also Saturday, Ukrainian Prime Minister Arseniy Yatsenyuk told Fox News there remained "a huge possibility that Russia could invade and seize Ukrainian territory."
Yatsenyuk also told Fox that there was reason for optimism after an hour-long phone call between President Obama and Russian President Vladimir Putin on Friday. "Diplomacy is always the best way forward," he said.
It was Putin's phone call — reports of which varied, depending on whether U.S. or Russian officials were delivering the details — that set off the latest efforts at diplomacy.
Russian officials said Putin had complained about activities of what he called "extremists" in Kiev, Ukraine's capital, and other regions.
Steven Pifer, a Russia expert at the Brookings Institute and a former U.S. ambassador to Ukraine, said Kerry's U-turn back to Europe was a good sign. But he expressed skepticism about Russia's moves and motives.
"It's a good thing that there's a conversation going," Pifer said. But he noted that "we continue to see the Russian massing of forces along the eastern Ukraine border. The question will be, does Lavrov have something new to say?"
What many foreign policy experts have called the gravest risk to East-West relations since the Cold War began just five weeks ago with the fall of Ukraine's pro-Russian president, Viktor Yanukovych, after months of protests.
Since then, Russia invaded and, after a hastily called referendum, annexed Crimea, an ethnic Russian region of Ukraine. U.S. and European nations, along with the United Nations and NATO, condemned the move and have imposed increasingly tough economic sanctions on Russian government leaders.