Donald Trump is to warn the future of the West is in doubt in speech in Poland ahead of a G20 meeting.
The warning, revealed by US officials, comes amid increasing tensions over North Korea and in the Gulf.
The president is expected to warn that the "fundamental question of our time is whether the West has the will to survive".
Mr Trump will address crowds in Warsaw and is expected to focus on the importance of Poland and security concerns facing the world. He will also talk about the US relationship with the EU, officials said.
Trump is delivering the speech from Krasinski Square, the site of a monument commemorating the 1944 Warsaw Uprising against Nazi occupation. Polish media reports said the government, as part of its invitation to Trump, promised the White House a reception of cheering crowds. Plans call for ruling party lawmakers and pro-government activists to bus in groups of people from outlying provinces for the speech.
The White House did not respond to requests for comment on those reports. Scores of people lined darkened streets late Wednesday after Trump arrived to watch as the motorcade sped him and his wife, Melania, to their hotel.
After the speech, the president will head to Germany for the meeting of the G20.
