BEIJING — China rolled out the red carpet for President Donald Trump on Thursday, treating him to an elaborate welcome ceremony on the plaza outside the Great Hall of the People before the leaders turned to their private talks.

But thorny issues await Trump and Chinese President Xi Jinping behind closed doors, including potential tensions over trade and China’s willingness to put the squeeze on North Korea over its nuclear weapons program.

Before arriving, Trump delivered a stern message to Beijing, using an address to the National Assembly in South Korea to call on nations to confront the North.

“All responsible nations must join forces to isolate the brutal regime of North Korea,” Trump said. “You cannot support, you cannot supply, you cannot accept.”

He called on “every nation, including China and Russia,” to fully implement U.N. Security Council resolutions against North Korea enforcing sanctions aimed at depriving its government of revenue for its nuclear and ballistic missile programs.

White House officials said Trump would underscore his public messages about North Korea when he and Xi sit down for private talks on Thursday.