(Charles Dharapak/AP Photo)

WARSAW - After an eight and a half hour flight, President Obama touched down in Warsaw, Poland Tuesday, starting his four-day tour through Europe where the topic of Ukraine will be high on the agenda.

The president was greeted by Polish President Bronislaw Komorowski at the Warsaw Chopin airport. The two leaders then toured an airplane hangar housing F-16s and greeted American and Polish troops.

Speaking before about 50 American and Polish soldiers, President Obama said the U.S. was committed to helping maintain the security of the region, calling it "sacrosanct."

"I'm starting the visit here because our commitment to Poland's security as well as the security of our allies in central and eastern Europe is a cornerstone of our own security and it is sacrosanct," President Obama said. ""It is a commitment that is particularly important at this point in time."

President Obama is asking Congress to support a $1 billion package to increase the U.S. security presence across Europe. The White House said this will include additional training, exercises and rotational presence across Europe, including rotations of U.S. air and ground troops.

The two presidents spoke in front of four F-16 fighter jets, two American and two Polish. In March, the U.S. sent 12 F-16 fighter jets and additional troops to Poland as a response to Russia's aggression in Ukraine. In April, U.S. Airborne Infantry paratroopers arrived in Poland to conduct bilateral and multilateral land force training and exercises with Polish troops.

President Obama said he would announce additional steps the United States will take to aid in Poland's security today and noted the American and Polish troops training in Poland are "part of the backbone of an alliance and a long history of Poles and Americans standing shoulder to shoulder for freedom."

As he closed out his speech, President Obama made a brief comment in Polish. He then shook hands with troops while Bruce Springsteen's song "Land of Hope and Dreams" played in the background.

Later in the day, President Obama will hold a news conference with President Komorowski as well as meet with Polish Prime Minister Donald Tusk.

The president will sit down for a meeting with eastern and central European leaders in the afternoon and is expected to discuss the United States' commitment to maintaining the security of their region. In the evening, President Obama will attend a Solidarity dinner at the Royal Castle ahead of the 25 th anniversary celebration on Wednesday of the first partially free elections in Poland.