The U.S. President said North Korea had behaved in a "very, very risky manner", and added: "I call on all nations to confront this global threat and publicly demonstrate to North Korea that there are consequences for their very, very bad behaviour".
He was talking about how the people of Poland dealt invasions from the west and the east when he blurted out: "In 1939 you were invaded yet again by Nazi Germany from the west, and the Soviet Union in the east". US and Polish flags were visible, with some people wearing "Make America Great Again" caps. "The fundamental question of our time is whether the West has the will to survive". "We (are) right now dealing with this very serious escalation, this provocation, this affront to the United Nations Security Council resolutions", he said.
The development comes amid the ongoing standoff between the West and Moscow over Russia's annexation of Ukraine's Crimean Peninsula back in 2014, and the ongoing pro-Russian insurgency in Ukraine's Donbass region since then. "Well I think it was Russian Federation and I think it could have been other people in other countries, could have been a lot of people interfered".
During his first trip as U.S. president, Trump was at the epicenter of accusations of a possible coalition with Moscow to interfere in the 2016 elections, which undermined his cabinet of advisors.
He added: "Nobody really knows for sure".
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Rogers' confident start belied her world ranking of 70, the American hitting twice as many winners as the top seed in the opening set.
Donald Trump has warned that the future of Western civilisation is at risk in a keynote speech ahead of the world leaders meeting at the G20 summit.
The US President began his four-day trip to Europe in the Polish capital of Warsaw, speaking in front of 10,000 people at Krasinski Square.
Trump arrives in Warsaw on Wednesday night. His discussion of terrorism and extremism was well-received by the generally pro-Duda crowd. "He's trying to bully us, and we're not going to let him intimidate us".
"We'll see what happens - I don't like to talk about what we have planned - but I have some pretty severe things that we're thinking about".
"We can not accept those who reject our values", Trump added, "and who use hatred to justify violence against the innocent".