HANOI, Vietnam — After exchanging praise over dinner, President Trump on Thursday morning opened a day of formal talks with Kim Jong-un, the leader of North Korea, a meeting aimed at once again trying to persuade the North to dismantle its nuclear weapons program and join the global economy.

“I can’t speak necessarily for today, but I can say a little bit longer term and over a period of time I know we are going to have a fantastic success with respect to Chairman Kim and North Korea,” Mr. Trump said.

“Speed is not important to me,” he added. “I very much appreciate not testing,” he said in referring to the North Koreans’ halt since late 2017 to its nuclear testing.

Mr. Kim, when asked by an American reporter whether he thought he would reach a deal with Mr. Trump, said: “ “It’s too early to say. I would not say I’m pessimistic.”