Story highlights Trump and Putin are set to speak on the phone Saturday

The President has suggested he may ease sanctions; the White House says that's not the plan

Washington (CNN) President Donald Trump's hints about easing sanctions on Russia have been met with a clear European response -- please don't.

On Saturday, Trump is set to hold his first official phone call with Russian President Vladimir Putin, a day after a senior aide said Trump is considering lifting penalties put in place after Russia's intervention in eastern Ukraine and annexation of Crimea.

British Prime Minister Theresa May, visiting Washington Friday, made clear the UK's position -- sanctions should remain until Russia and the Ukrainian rebels it backs meet the requirements of a 2014 agreement to end hostilities.

If the US moves forward on sanctions without the backing of allies like the UK, Trump risks seriously straining ties with some of its oldest and most reliable allies, European countries are already unsettled by the President's stated desire to get closer to Russia and his suggestions that NATO is "obsolete."

Unilaterally easing Russia sanctions "would be another blow to US-EU relations," said Angela Stent, director of the Center for Eurasian, Russian and East European Studies at Georgetown University. "If sanctions are removed unilaterally it removes a major basis for trust between the two allies."

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