U.S. Treasury Secretary Janet Yellen paid a surprise visit to Kyiv on Monday to reaffirm U.S. support for Ukraine in its struggle against Russia's invasion and promote U.S. economic aid that is bolstering Ukraine's war effort.

Yellen met with President Volodymyr Zelenskyy, Finance Minister Serhiy Marchenko and other key government officials just days into the war's second year, repeating U.S. assurances delivered by President Joe Biden a week ago in Kyiv.

"America will stand with Ukraine as long as it takes," Yellen, flanked by sandbags at the cabinet ministers' office, told Ukrainian Prime Minister Denys Shmyhal, in a trip also aimed at shoring up support at home for continued aid.