LONDON and KYIV -- President Joe Biden on Monday made an unannounced visit to war-torn Ukraine, arriving in Kyiv as the United States signals its ongoing support ahead of the anniversary of Russia's invasion.
Biden planned to meet for extended discussions with President Volodymyr Zelenskyy and other officials, he said in a statement. He also planned to announced delivery of "critical equipment, including artillery ammunition, anti-armor systems, and air surveillance radars."
Biden's arrival in Kyiv -- a city the Ukrainians successfully defended early in the war -- was marked by an increased security presence, with downtown blocks brought to a standstill by police and military vehicles. He was also met with air raid sirens, a near constant sound in a city where civilians have often been targeted by Russian President Vladimir Putin's missiles.
"When Putin launched his invasion nearly one year ago, he thought Ukraine was weak and the West was divided," Biden said in a statement. "He thought he could outlast us. But he was dead wrong."
He said the visit reaffirmed that the United States has "unwavering and unflagging commitment to Ukraine's democracy, sovereignty and territorial integrity."
Biden administration officials later briefed reporters on some aspects of how the trip came together. They stressed that it was the president's call to take a strategic risk to show support for Ukraine once he believed that the security threat was manageable.
And while the officials remained tight-lipped about the precise details required to manage the trip, including Biden's mode of transportation in and out of the country, they did say that the U.S. informed Russia of the visit shortly before Biden left for Ukraine.
"We did notify the Russians that President Biden would be traveling to Kyiv. We did so some hours before his departure for deconfliction purposes," Jake Sullivan, the national security adviser to the president, told reporters on Monday morning in a press briefing.
Biden's visit comes ahead of a planned meeting with NATO allies in Poland. He's scheduled on Tuesday evening to give a speech at the Royal Castle Arcades in Warsaw.
His remarks in Poland are expected to offer an appraisal of international support during the first year of the war, White House spokesperson Karine Jean-Pierre said in a statement earlier this month. He'll also address "how we will continue to stand with the people of Ukraine for as long as it takes," she said.
Biden's also plans to meet in Poland with leaders of the Bucharest Nine, a group of eastern NATO allies formed in 2015 in response to Russia's annexation of Crimea.
Ukrainian officials had accused Russia of planning "large-scale nuclear exercises" to coincide with Biden's European visit.
Biden's surprise visit comes two months after Zelenskyy's December address to Congress in Washington. That marked Zelenskyy's first known international trip since the invasion began in February 2022.
The Ukrainian leader had sought further U.S. aid for the fight against Russia, telling lawmakers that they could "speed up our victory."
"Your money is not charity. It's an investment in the global security and democracy that we handle in the most responsible way," Zelesnkyy said at the time.
Biden in January approved additional military aid to Ukraine, including sending 31 Abrams tanks. Those weapons would help Ukraine "achieve its strategic objectives," Biden said.
Rep. Nancy Pelosi as House speaker had led a group of U.S. lawmakers on a similarly unannounced visit to Kyiv, the capital, in May 2022.
"Our delegation traveled to Kyiv to send an unmistakable and resounding message to the entire world: America stands firmly with Ukraine," she said in a statement at the time.
ABC News' Justin Fishel, Jonathan Greenberger, Cheyenne Haslett, Lauren Minore and Molly Nagle contributed to this report.