President Biden met with Polish President Andrzej Duda in Warsaw on Tuesday, following Biden’s surprise visit to Kyiv, Ukraine, the day prior.

Biden and Duda met at the Presidential Palace, where a band played the U.S. national anthem upon Biden’s arrival. The band then played the Polish national anthem and the two presidents walked through a line of Polish military members before walking into the palace.

“A year later, I would argue NATO is stronger than it’s ever been,” Biden said in the meeting. “If we keep our head and we are focused, I think we’re in a better position than we’ve ever been.”

“This is a critical, critical, critical relationship to the United States and we thank you for all your cooperation and help,” Biden said.

The face-to-face meeting with Duda comes ahead of the one-year anniversary of Russia’s unprovoked invasion of Ukraine. Biden will make remarks from Warsaw on the war in Ukraine later on Tuesday.

Duda said Biden’s trip into Ukraine the day prior was a “political signal” that the free world is with Ukraine and the visit “boosted their morale,” referring to the Ukrainians.

“I can imagine it was not easy, especially for all those who are responsible for our security, sir,” Duda added. “All of us were looking at what you did yesterday.”

The Polish president thanked Biden for choosing Warsaw to give his speech on Tuesday.

“I’m sure that the whole world is going to follow your speech,” he said.

“It proves that Poland is safe and secure,” Duda added. “Thanks to the presence of the U.S armed forces, thanks to the presence of NATO troops.”

Biden spoke to Duda in November after Russian missiles crossed Poland’s border with Ukraine and killed two people in Poland. Biden at the time reiterated the “ironclad commitment” of the United States to the NATO alliance.

Biden arrived in Warsaw late Monday after his historic visit to war-torn Kyiv. He took a train for about 10 hours to get back into Poland from Kyiv and then took a short flight to Warsaw.

In Kyiv, Biden met with Ukrainian President Volodymyr Zelensky and announced $500 million in new military assistance for the country. Biden spent roughly five hours in the city for his first trip there since the war began.

The president’s trip to Kyiv took place under a shroud of secrecy and was unannounced until his arrival in the Ukrainian capital. The White House meticulously planned over months how to get Biden in and out of a war zone. His visit differed from past presidential visits to war zones like Iraq and Afghanistan because the U.S. does not have an established military presence on the ground in Ukraine.

Updated at 8:43 a.m.