Ukraine's frontlines were relatively calm on Sunday ahead of high-level EU-mediated gas talks between Kiev and Moscow, as journalists mourned the killing by mortar fire of a Ukrainian photographer.

Kiev's security officials said there was no fire after midnight on Ukraine's positions and no Ukrainian soldiers have been killed over the past 24 hours. 

International monitors said the conflict in Ukraine was at a "crossroads" as further losses among government forces rattled a two-week-old truce just as it seemed to be gaining traction.

The deaths of three Ukrainian soldiers after a two-day lull in clashes with pro-Russian separatists highlighted the fragility of the ceasefire as the U.N. said some five million people needed humanitarian aid due to the conflict.

Western leaders and Russia's opposition on Saturday condemned the drive-by assassination of Kremlin critic Boris Nemtsov while President Vladimir Putin suggested the crime was staged to throw suspicion on the state.  

U.S. President Barack Obama decried the "brutal" and "vicious murder" of Nemtsov, which prompted the cancellation of a major opposition rally planned for Sunday, and urged Russia to conduct an impartial probe.

International monitors said Friday the conflict in Ukraine was at a "crossroads" as further losses among government forces rattled a two-week-old truce just as it seemed to be gaining traction.

The deaths of three Ukrainian soldiers after a two-day lull in clashes with pro-Russian separatists highlighted the fragility of the ceasefire.

Exiled Russian former tycoon Mikhail Khodorkovsky warned on Friday that Vladimir Putin's policies in the Ukraine conflict will bring Russia to ruin, much as the Afghan war helped bankrupt the Soviet Union.

A year after annexing Crimea in Ukraine, Russia finds itself isolated and on a path to self-destruction, said Khodorkovsky, one of Putin's most outspoken critics, who spent a decade in prison on what he said were politically motivated charges.

The authorities in Russian-annexed Crimea said Friday they have nationalized film studios in the Black Sea resort of Yalta, famous for Soviet productions including Andrei Tarkovsky's classic "Solaris".

Crimea's State Council, the ruling regional body, passed a resolution saying the studios have been incorporated "into the property of the republic." 

Rebel fighters with Kalashnikovs watched over a dust-covered group of captured Ukrainian soldiers as they searched with their hands through the apocalyptic jumble of smashed concrete and twisted metal that is Donetsk airport.

The task of the 18 captives was a grim one.

Ukraine said on Friday three soldiers had been killed, the first fatalities in several days in the war-torn east, as a shaky truce with pro-Russian rebels appeared to gain some traction with an apparent weapons pull-back.

Isolated skirmishes highlighted the fragile situation as the U.N. discussed the conflict exactly one year after Russia and pro-Moscow forces began seizing ports and cities on the Black Sea peninsula of Crimea.

Police arrested eight Spanish men who returned from fighting alongside pro-Russian forces in eastern Ukraine, in what they said was the first operation of its kind in Europe.

Officers detained the suspects in six regions across Spain after they returned from predominantly Russian-speaking eastern Ukraine, the interior ministry said in a statement.

A Ukrainian airforce pilot, who has been on hunger strike in a Russian prison for 77 days, "could die within days," a member of the Kremlin's human rights council said Friday.

Nadia Savchenko, a 33-year-old helicopter navigator, who has been charged with involvement in the deaths of two Russian reporters in a mortar attack in east Ukraine, has been held in a Moscow jail for nearly nine months.