President Joe Biden made a surprise trip to Ukraine on Monday to "reaffirm" U.S. support for the country as it enters the second year of its war against Russia.

"I am in Kyiv today to meet with President Zelenskyy and reaffirm our unwavering and unflagging commitment to Ukraine's democracy, sovereignty and territorial integrity," Biden, 80, said in a written statement.

"When Putin launched his invasion nearly one year ago, he thought Ukraine was weak and the West was divided," he continued. "He thought he could outlast us. But he was dead wrong."

AP Photo/Evan Vucci, Pool Jo Biden visits Kyiv

Zelenskyy, 45, welcomed the president to his country on the social media site Telegram and posted a photo of the two leaders.

"Joseph Biden, welcome to Kyiv!" Zelenskyy wrote. "Your visit is an extremely important sign of support for all Ukrainians."

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Photo by Ukrainian Presidential Press Office via Getty Images Joe Biden visits Kyiv

NBC News reported that Biden's visit was also the first time in modern history that a sitting U.S. president has visited an active war zone with no active American military presence.

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Biden and Zelenskyy made brief remarks at the Mariinsky Palace, where he signed the guest book, per NBC News. He also paid a visit to St. Michael's Golden-Domed Monastery, the nearby Wall of Remembrance and the U.S. embassy.

A portion of central Kyiv was shut down as police and the country's military lent additional security to Biden's visit, reported ABC News.

DIMITAR DILKOFF/AFP via Getty Images Joe Biden visits Kyiv

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Ahead of his remarks, Biden said in his statement that the U.S. will continue to support the war-torn country and announced an aid package of $500 million, including artillery ammunition, anti-armor systems and air surveillance radars.

"Over the last year, the United States has built a coalition of nations from the Atlantic to the Pacific to help defend Ukraine with unprecedented military, economic, and humanitarian support – and that support will endure," he added.

Photo by UKRAINIAN PRESIDENTIAL PRESS SERVICE HANDOUT/EPA-EFE/Shutterstock

Biden's overseas trip will continue on to Poland, where he is scheduled to meet President Andrzej Duda and other Eastern European allies to "continue to rally the world to support the people of Ukraine and the core values of human rights and dignity in the UN Charter that unite us worldwide," the president added in his statement.

The Russian attack on Ukraine is an evolving story, with information changing quickly. Follow PEOPLE's complete coverage of the war here, including stories from citizens on the ground and ways to help.