NATO has warned that there will “more deaths, more suffering and more destruction” in coming days in Ukraine.
The alliance’s Secretary-General, Jens Stoltenberg, called on Russian President Vladimir Putin to withdraw all troops from Ukraine without conditions.
“The days to come are likely to be worse, with more deaths, more suffering and more destruction,” he said after a meeting of the alliance’s foreign ministers in Brussels.
Mr Stoltenberg also confirmed reports of cluster bombs being used against civilians in Ukraine in breach of international law.
Putin issues fresh warning; follow Ukraine updates live
He added: “This is President Putin’s war. One he has chosen, planned, and is waging against a peaceful country.
“We call on President Putin to stop this war immediately, withdraw all his forces from Ukraine, and engage in genuine diplomacy now.”
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He ruled out putting NATO planes in Ukrainian airspace, troops on the country’s soil, or establishing a no-fly zone, saying the alliance is not seeking war with Russia.
NATO is “not part of this conflict”, he added, but has a “responsibility to ensure it does not escalate and spread beyond Ukraine”.
He claimed direct NATO involvement would result in a situation more “devastating and dangerous” than it is now.
Mr Stoltenberg’s comments came after Russian forces hit Ukraine’s Zaporizhzhia nuclear power plant overnight, which he described as “reckless”.
Three Ukrainian soldiers were killed after the plant – the biggest in Europe – caught on fire. Russia has now claimed control of the facility, as it did with the defunct one at Chernobyl last week.
Speaking after Ukrainian foreign minister Dmytro Kuleba met his NATO counterparts, Mr Stoltenberg said that while NATO forces won’t be deployed in Ukraine they have been stepped up across eastern Europe – particularly in Georgia and Bosnia and Herzegovina.
NATO’s response force is being deployed for the first time, he added, and 130 jets and 200 ships are on “high alert” across Europe.
Meanwhile, in a new address, Mr Putin asked Russia’s neighbours to “normalise relations” with the Kremlin.
“There are no bad intentions towards our neighbours,” he said.
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Warning them “not to escalate the situation”, he added: “All our actions, if they arise, they always arise exclusively in response to some unfriendly actions, actions against the Russian Federation.”
As Mr Stoltenberg warned that “Russia is paying the price” for its “renewed aggression”, the UK announced sanctions against two further oligarchs.
Alisher Usmanov and Igor Shuvalov, who have a combined net worth of £19bn (£14.3bn), will now face asset freezes and travel bans.