Warsaw, Poland (CNN) President Donald Trump chided North Korea for its recent missile tests, saying it is "behaving in a very very dangerous manner."

"It's a shame they're behaving this way -- they're behaving in a very, very dangerous manner and something will have to be done about it," Trump said in a news conference Thursday with Polish President Andrzej Duda.

The President said he has "some pretty severe things" available to him when asked about military action against North Korea, but declined to elaborate.

"As far as North Korea is concerned, I don't know, we will see what happens," Trump said when asked about military action against North Korea. "I have some pretty severe things that we are thinking about. That doesn't mean we are going to do it. I don't draw red lines."

Trump's comments came after North Korea launched what is believed to be its first test of an intercontinental ballistic missile Tuesday. US officials estimate it had a range of 3,400 miles, capable of hitting Alaska.

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At a special meeting of the United Nations Security Council Wednesday, US Ambassador to the UN Nikki Haley warned military action was on the table in response to the test. "The US is prepared to use the full range of our capabilities to defend ourselves and our allies," she said, adding the US would "prefer not" to use force. She called on China to use its economic influence over North Korea to rein in the regime of King Jong Un.

In his first comments since North Korea's missile launch, Defense Secretary James Mattis said Thursday he does not "believe this capability itself brings us closer to war" and that the US would continue with diplomatic efforts.

Mattis went on to call North Korea's launch a "serious escalation" and "provocation." He also said as soon as they saw the missile launch and its trajectory, officials knew it was not aimed directly at the US.

Trump also mentioned his 2016 election victory early in his opening statement, touting Polish Americans for backing him in 2016 as Duda stood next to him.

"As you know, Polish Americans came out in droves in the last election and I was very happy with that result," Trump said.

The press conference outside Warsaw's Royal Castle was Trump's first since June 9, when the Romanian President visited the White House.

The President did not mention the arms deal struck overnight in Warsaw. Poland's Defense Minister Antoni Macierewicz told reporters on Thursday that the United States had agreed to sell Patriot missiles to Poland.

Populist tone in speech to Polish people

Trump will strike a populist tone in Poland on Thursday, decrying "the steady creep of government bureaucracy" and casting the story of Poland as one of people "who have never forgotten who they are," according to excerpts of the speech to the Polish people Trump plans to deliver.

The speech, along with his meeting with Duda and a session with other Eastern European leaders on energy infrastructure investment, kicks off Trump's second trip abroad as president, a critically important trip that will later see Trump discuss trade, climate and migration at the G20 meeting in Germany.

Trump is expected to receive a warm welcome in Poland, where American presidents have long been well received and whose conservative government, led by Duda, is more ideologically in line with Trump than his predecessor, Barack Obama.

"I am here today not just to visit an old ally, but to hold it up as an example for others who seek freedom and who wish to summon the courage and the will to defend our civilization," Trump plans to say in his high-profile speech to the Polish people from Krasinski Square.

The speech will be symbolic for Trump: Standing in the square, the President will be flanked by the Warsaw Uprising Monument, a large memorial that remembers the Poles who fought to free Warsaw from Nazi control in 1944.

"The triumph of the Polish spirit over centuries of hardship gives us all hope for a future in which good conquers evil, and peace achieves victory over war," Trump plans to say. "The story of Poland is the story of a people who have never lost hope, who have never been broken, and who have never forgotten who they are."

Poland's ruling Law and Justice Party has worked to ensure Trump is greeted warmly in Poland. Conservative politicians from around Poland have informed constituents that they will provide free buses from cities as far away as a 4-hour drive so that people can watch Trump's speech.

Contentious G20 meeting is next

Trump's visit to Poland will be short. After landing in Warsaw on Wednesday night, Trump leaves on Thursday afternoon for Hamburg Germany and the G20 meeting. In total, Trump will spend around five working hours in Warsaw.

Thursday's visit to Warsaw opens a trip that will see the President meet face-to-face with Russian President Vladimir Putin. Russian meddling in the 2016 election and investigations into the Trump campaign's connections to Russian operatives have hung over the White House for months.

The G20 meeting in Hamburg will be a contentious affair with a host of confrontations on the schedule.

Looming over the whole conference will be Trump's meeting with Putin, which will likely be analyzed worldwide for changes in American policy to Russia.

After the day in Poland, Trump flies to Hamburg, where he will meet with German Chancellor Angela Merkel, who has maintained an icy relationship with Trump since they met at the White House in March.

Merkel all but ensured the G20 meeting in Hamburg will be combative when she put trade, climate change and migration on the agenda for the meeting, all topics about which she and other world leaders have publicly sparred with Trump.