A Moscow court has jailed an ex-policeman for 15 years for high treason after he was caught placing documents under a fake rock, allegedly for the CIA, in the latest such case in Russia.

Roman Ushakov was found guilty and sentenced Thursday for trying to transmit coded documents from the Russian interior ministry to the United States' Central Intelligence Agency, Russian news agencies reported.

EU foreign ministers on Friday downplayed the threat of new sanctions against Russia but warned they remain on the table if Moscow undermined the latest Ukraine ceasefire accord.

France and Germany brokered a second Minsk peace agreement with Russia and Ukraine last month which so far seems to be holding, though the situation remains fragile and the outlook for full implementation is uncertain.

The European Union lifted sanctions on Friday against four Ukrainians including the son of a former premier, while extending measures against ousted president Viktor Yanukovych and 14 others for a year.

Brussels ended the travel ban and asset freeze imposed one year ago on Oleksii Azarov, the son of ex-prime minister Mykola Azarov, although his father remains on the list, according to the EU official journal.

Top Kremlin critic Alexei Navalny on Friday vowed to keep up his fight against President Vladimir Putin as he was released from his latest jail term, a two-week stint for organizing an illegal gathering.

The charismatic opposition leader also said he would pay a visit to the cemetery where outspoken activist Boris Nemtsov was buried after being gunned down last week near the Kremlin.

Italian Prime Minister Matteo Renzi said Thursday Russia could play a decisive role in resolving the crisis in Libya, during a rare visit by a European leader to Moscow.

Renzi held talks with President Vladimir Putin in a visit that also focused on the conflict in Ukraine and Russia's chilly relations with the European Union over its backing of  separatist rebels in eastern Ukraine.

A Spanish court on Thursday remanded in custody Ukraine's former finance minister Yuri Kolobov pending his extradition to Kiev where he is wanted for alleged fraud and theft of public funds.

Police detained Kolobov, who served under ousted president Viktor Yanukovych, on Wednesday in Altea, a hilltop village on the Mediterranean coast in the province of Alicante.

The U.N. Security Council will meet Friday to take stock of the latest efforts to prop up a ceasefire in east Ukraine, diplomats said.

The 15-member council has endorsed the February 15 ceasefire reached between Russia, Ukraine, France and Germany to end the 10-month conflict, Europe's worst since the war in the Balkans in the 1990s.

Russian officials on Thursday dismissed a claim by the United States that Moscow has sent "thousands" of troops to fight alongside pro-Russian separatists in Ukraine.

"These figures, which are plucked out of the air, of course demoralize and disorientate the international community," foreign ministry spokesman Alexander Lukashevich said.

Ukraine on Thursday observed a day of mourning after 32 miners perished in a blast in a notoriously dangerous mine just a few kilometers from the frontline, where Kiev is reporting an increase in attacks by pro-Russian separatists.

Rescuers found the bodies of 32 miners in the Zasyadko mine, with one person unaccounted for, a day after a blast ripped through the shaft, emergency officials of the self-proclaimed Donetsk People's Republic said.

Rescuers found 32 bodies of miners in the Zasyadko mine in eastern Ukraine a day after a blast ripped through the shaft, a rebel official said on Thursday.

"32 bodies of dead miners of the Zasyadko mine have been found" by early morning, the emergency ministry of the self-proclaimed Donetsk People's Republic said in a statement, adding that the bodies were being raised to the surface.