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TOP WRAP 3-Ukraine negotiations to resume, Europe faces Russia gas deadline

(Adds IEA emergency meeting, Russian troops pull back from Kyiv)

* Talks resume, humanitarian corridor for Mariupol to open

* Moscow demands European gas buyers pay in roubles

* Europe says it will not be 'blackmailed'

* Zelenskiy points to 'battles ahead' in Donbas

By Vitalii Hnidyi and Pavel Polityuk

TROSTYANETS/LVIV, Ukraine, April 1 (Reuters) - European buyers of Russian gas faced a deadline to start paying in roubles on Friday, while negotiations aimed at ending the five-week war were set to resume even as Ukraine braced for further attacks in the south and east.

Moscow's invasion of its neighbour has killed thousands, sent millions fleeing and galvanised the United States and allies around the world to impose punishing penalties on Russian government entities, businesses and oligarchs.

Russia will respond to European Union sanctions, the RIA news agency quoted a senior foreign ministry official on Friday.

"The actions of the EU will not remain unanswered ... the irresponsible sanctions by Brussels are already negatively affecting the daily lives of ordinary Europeans," Nikolai Kobrinets told the news agency.

Russian President Vladimir Putin played one of his biggest cards on Thursday, demanding European energy buyers start paying in roubles from Friday or have existing contracts halted.

European governments rejected Putin's energy ultimatum, with the continent's biggest recipient of Russian gas, Germany, calling it "blackmail".

The energy showdown has huge ramifications for Europe as U.S. officials circle the globe to keep pressure on Putin to stop an invasion that has uprooted a quarter of Ukraine's 44 million people.

The International Energy Agency will hold an emergency meeting on Friday to discuss a new release of strategic oil reserves alongside a U.S. plan to pump massive supplies starting in May to cool soaring oil prices. The Ukraine war has seen oil prices soared more than 30% this year.

The war also threatens to disrupt global food supplies, with a U.S. government official sharing images of what they said was damage to grain storage facilities in Ukraine, a major grain exporter.

'BATTLES AHEAD'

Putin sent troops on Feb. 24 for what he calls a "special military operation" to demilitarise Ukraine. Western countries say Putin's real aim was to topple Ukraine's government.

At talks this week, Moscow said it would reduce offensives near the capital Kyiv and in the north as a goodwill gesture and focus on "liberating" the southeastern Donbas region.