President Joe Biden has pledged ahead of the first face-to-face meeting with Vladimir Putin of his administration that the US will stand with its European allies against Russia.

Biden will head to Europe Wednesday, and plans to attend both the G-7 and NATO summits as well as holding a high-stakes meeting with the Russian leader in Geneva on June 16.

The summit comes amid the largest crisis in relations between the two countries in years, with tensions high over a litany of issues including hacking allegations, human rights and claims of election meddling.

In an op-ed for the Washington Post published Saturday, the US president pledged to shore up Washington’s “democratic alliances” in the face of multiple crises and mounting threats from Moscow and Beijing.

“We are standing united to address Russia’s challenges to European security, starting with its aggression in Ukraine, and there will be no doubt about the resolve of the United States to defend our democratic values, which we cannot separate from our interests,” he wrote.

“President Putin knows that I will not hesitate to respond to future harmful activities,” he said. “When we meet, I will again emphasize the commitment of the United States, Europe and like-minded democracies to stand up for human rights and dignity.”

Since taking office in January, Biden has ramped up pressure on the Kremlin, and his comments likening Putin to a “killer” were met with severe criticism in Moscow.

But both leaders have expressed hopes that ties can improve, with the Russian president saying Friday he expected a “positive” result from the talks.