WARSAW, Feb. 21 - President Joe Biden on Tuesday warned of “hard and bitter days ahead” as Russia’s invasion of Ukraine nears the one-year mark, but vowed that no matter what, the United States and allies “will not waver” in supporting the Ukrainians.

A day after his surprise visit to Kyiv, Biden used a strongly worded address in neighboring Poland to praise allies in Europe for stepping up over the past year and to send a clear message to Russian President Vladimir Putin that “NATO will not be divided, and we will not tire,” The Associated Press reported.