President Trump, swiftly dismantling decades of U.S. government policy that treated Syria like a pariah, held an extraordinary meeting on Wednesday with its president, Ahmed al-Shara, the former leader of a rebel group designated as a terrorist organization by the American government.

The meeting, held in Riyadh, Saudi Arabia, at the urging of Crown Prince Mohammed bin Salman, occurred a day after Mr. Trump announced that he was lifting sweeping sanctions against Syria, which Washington began imposing in 1979.

Mr. Trump, who has been known to assess people according to how they look, suggested that Mr. al-Shara, a rugged figure with a thick black beard who toppled the brutal Assad dynasty in December, had made a favorable impression.

“Young, attractive guy,” Mr. Trump described him to the news media. “Tough guy. Strong past. Very strong past. Fighter.”

“He’s got a real shot at pulling it together,” Mr. Trump said of Syria, adding, “It’s a torn-up country.”

The last meeting between the leaders of both countries occurred 25 years ago.

Mr. Trump spoke as he flew to Qatar, the second stop on his four-day, three-nation Middle East tour that will take him next to the United Arab Emirates. The Qataris, like the Saudis, greeted Mr. Trump with pomp, including an honor guard mounted on camels for his presidential motorcade.