Diplomats from Russia, the United States, the European Union and Ukraine have agreed on a series of steps aimed at de-escalating violence in strife-ridden Ukraine, U.S. Secretary of State John Kerry says.

Speaking at a news conference on Thursday in Geneva, Kerry said all of this "represents a good day's work." But Kerry added "words on paper" will have little meaning if they are not followed by actions on all sides to calm the situation in the former Soviet republic.

Kerry said the U.S. fully expects the Russians" to demonstrate they are serious about lowering tensions. 

He added that he's told his Russian counterpart, Sergey Lavrov, that if no improvement is seen, "We will have no choice but to impose" increasing sanctions against Russia.

UN Secretary-General Ban Ki-moon issued a news release welcoming the agreement, calling it an encouraging development in the ongoing crisis.

Ban said the situation in Ukraine remains “extremely volatile” and called on Russia and the West to continue to meet in good faith until a solution is found. 

The deal comes after Ukraine appeared to introduce stringent checks for Russian citizens who want to cross the border into Ukraine.

Russia's flagship Aeroflot said Thursday that Ukrainian officials told the airline that Russian men between 16 and 60 are now banned from entering Ukraine except when they are travelling with family or to funerals of relatives there.

Serhiy Astakhov, an aide to the Ukrainian Border Guard Service chief, told The Associated Press he was "not aware" of the ban mentioned by Aeroflot. Still he admitted that "in the light of the anti-terrorist operation underway in this country, we are introducing certain restrictions."

Astakhov would not elaborate on the restrictions. He said Ukraine is now checking travelers more stringently but granting admittance into the country has always been decided on an individual basis.

Putin hopes for diplomatic solution

Earlier Thursday, Russian President Vladimir Putin rejected claims that Russian special forces are fomenting unrest in eastern Ukraine, but recognized for the first time that the troops in unmarked uniforms who had overtaken Ukraine's Crimean Peninsula before its annexation by Moscow were Russian soldiers.

Putin expressed hope for a political and diplomatic solution of the worst East-West crisis since the Cold War, saying he hopes that he won't have to send Russian troops into eastern Ukraine, which has been engulfed by violent protests against the new authorities in Kyiv. He poured scorn at the West, accusing it of trying to weaken and isolate Russia and made it starkly clear that he doesn't fear further Western sanctions.

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Russian President Vladimir Putin takes part in a live broadcast nationwide phone-in in Moscow. He said that people in eastern Ukraine have risen against the authorities in Kyiv. (Alexei Nikolskyi/Reuters)

Speaking in a televised call-in show with the nation, Putin harshly criticized the West for trying to pull Ukraine into its orbit and said that people in eastern Ukraine have risen against the authorities in Kyiv, who ignored their rights and legitimate demands.

A wave of protests, which Ukraine and the West said was organized by Russia and involved Russian special forces, have swept eastern Ukraine over the past weeks, with gunmen seizing government offices and police stations in at least 10 cities.

"It's all nonsense, there are no Russian units, special services or instructors in the east of Ukraine," Putin said.

At the same time, he recognized for the first time that soldiers in unmarked uniforms — dubbed "little green men" — who swept Ukraine's Black Sea region of Crimea laying the ground for its annexation by Moscow last month were Russian troops.

'They acted politely'

Putin, who previously said the troops were part of local self-defence forces, said the Russian soldiers' presence was necessary to protect the local population from armed radicals and to ensure the holding of a referendum, in which an overwhelming majority of its residents voted for seceding from Ukraine and joining Russia.

But asked on Thursday who the men in unmarked uniforms were, Putin said they were Russian servicemen who "stood behind the back of Crimea's self-defence forces."

"They acted politely, but resolutely and professionally," he said. "There was no other way to hold the referendum in an open, honest and honourable way and allow the people to express their opinion."

With files from CBC News