U.S. president didn’t say what steps he might take or whether he is thinking of military response

Peter Nicholas and
Anton Troianovski

WARSAW—President Donald Trump said Thursday he is considering “some pretty severe things” in response to North Korea’s continued efforts to develop nuclear weapons that can reach the U.S.

At a joint news conference with his Polish counterpart, Andrzej Duda, Mr. Trump said that North Korean leaders were “behaving in a very, very dangerous manner and something will have to be done about it.” He didn’t say what steps he might take or if he is contemplating military action.

On the eve of Independence Day in the U.S., North Korea test-fired an intercontinental ballistic missile, an advance that could render the U.S. vulnerable to a nuclear attack.

Military reprisal by the U.S. carries risks, and Mr. Trump has sought other avenues to choke off North Korea’s nuclear program—notably, persuading China to use its influence to rein in Pyongyang.

Mr. Trump arrived in Poland late Wednesday for a series of meetings before heading to a Group of 20 summit meeting in Germany. He will meet in Hamburg with his Chinese counterpart Xi Jinping, a forum where he is expected to make the case for more aggressive Chinese intervention.

After warning of “severe” actions against North Korea, Mr. Trump hastened to add: “That doesn’t mean we’re going to do them.”

“I think we will just take a look at what happens over the coming weeks and months with respect to North Korea,” Mr. Trump added.

Mr. Trump later held a speech in front of thousands of Poles in which he cast the U.S. and Poland as waging a common battle in defense of Western civilization.

In Krasinski Square, scene of a Polish uprising against the Nazis in 1944, he singled out both Islamist extremism as well as the “steady creep of government bureaucracy.”

He said that America’s words and actions demonstrated that the country stood firmly behind the mutual defense commitment of the North Atlantic Treaty Organization.

“The fundamental question of our time is whether the West has the will to survive,” Mr. Trump said. “Just as Poland cannot be broken, I declare today, for the world to hear, that the West will never, ever be broken… Our civilization will triumph.”

Mr. Trump’s speech echoed a critique of the European Union often uttered by Poland’s conservative governing party as well as by nationalist, anti-EU parties across the continent.

“The West became great not because of paperwork and regulations but because people were allowed to chase their dreams and pursue their destinies,” Mr. Trump said. “Americans, Poles, and nations of Europe value individual freedom and sovereignty.”

At the news conference, Mr. Trump also fielded questions about whether he accepts the U.S. intelligence community’s verdict that Russia interfered in the 2016 election in a bid to help him defeat Democratic rival Hillary Clinton.

The issue has fresh urgency, with Mr. Trump set to meet Russian President Vladimir Putin on Friday at the summit, the first time the two have met face to face since Mr. Trump’s election victory in November.

President Donald Trump gestures during a joint news conference with Polish President Andrzej Duda in Warsaw.

President Donald Trump gestures during a joint news conference with Polish President Andrzej Duda in Warsaw. Photo: CARLOS BARRIA/REUTERS

The meeting takes place against a backdrop of the intensifying federal investigation into Russian meddling. Special Prosecutor Robert Mueller is also probing whether Trump campaign aides colluded with Russian operatives to boost Mr. Trump’s prospects and damage Mrs. Clinton.

Mr. Trump has in the past voiced skepticism about Russia’s involvement. He said once again that others might have been culpable, apart from Russia.

“I think it was Russia and I think it could have been other people and other countries,” Mr. Trump said. “A lot of people interfered. I think it’s been happening for a long time.”

Mr. Trump also said the U.S. intelligence community has made mistakes in the past and its judgment is open to question. As he has done in the past when discussing Russian hacking, he mentioned the U.S. invasion of Iraq in 2003. Intelligence assessments claiming that Iraq possessed weapons of mass destruction turned out to be inaccurate.

“I remember listening about Iraq,” Mr. Trump said.

He added: “Nobody really knows. Nobody really knows for sure.”

Many congressmen want Mr. Trump to confront Mr. Putin about what intelligence officials say is conclusive proof that Russia hacked Democratic computer systems in a bid to influence the election.

The White House has not confirmed whether Mr. Trump will bring it up.

Mr. Trump also took a swipe at his predecessor, Barack Obama. Invoking news reports that Mr. Obama was told about Russian hacking last August, Mr. Trump said the former president took no action because of the mistaken belief that Mrs. Clinton would win anyway.

Mr. Trump now flies to Hamburg for the two-day G-20 summit. After touching down in Germany he will hold a bilateral meeting with the nation’s chancellor, Angela Merkel.

The session is expected to be tense, with the chancellor having made plain her unhappiness over Mr. Trump’s withdrawal from the Paris climate accord. No apology is likely, though Mr. Trump is open to a new or revamped climate agreement if he concludes it is in America’s interests, White House officials said.