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.

Excluding Russia from the SWIFT banking system would be a measure of last resort if the crisis in Ukraine escalates, the British and Polish foreign ministers said Friday. 

"When it comes to sanctions, SWIFT is the nuclear weapon. It is the last resort and we are all aware of that," Polish Foreign Minister Grzegorz Schetyna said at a joint press conference in Warsaw with British counterpart Philip Hammond.

The Ukrainian girlfriend of murdered Russian opposition activist Boris Nemtsov, who was by his side when he was shot dead, has complained to police of receiving death threats, Ukrainian prosecutors said on Friday.

"Ganna Duritska... filed a statement about the threat to her life from unidentified people during her time in her parents' home" where she has stayed since her return Monday to Kiev from Moscow, said a statement from the prosecutor general. 

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.

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.

The United States is pushing the U.N. Security Council to threaten tough measures against the Syrian regime over its alleged use of chlorine in attacks, according to a draft resolution circulated to members on Wednesday.

The text obtained by Agence France Presse states that the Security Council "decides in the event of future non-compliance... to impose measures under chapter 7" of the U.N. charter, which provides for sanctions and possibly military force.

Spanish police on Wednesday detained Ukraine's former finance minister Yuri Kolobov who is wanted by Kiev for alleged fraud and theft of public funds, a police source said.

The 41-year-old, who served under ousted pro-Kremlin president Viktor Yanukovych, was arrested in Altea, a hilltop village on the Mediterranean coast, the source said.

The United States' senior envoy to Europe alleged Wednesday that Russia had deployed "thousands and thousands" of troops to neighboring Ukraine.

Speaking to a congressional foreign affairs committee, Assistant Secretary of State Victoria Nuland also told U.S. lawmakers that Russia was flooding eastern Ukraine with military hardware.