SEOUL, South Korea — China, Japan and Russia — North Korea’s neighbors — while offering praise for the summit meeting with South Korea that riveted the world this week, appeared to acknowledge one thing: Now comes the hard part.

Some analysts and media commentators expressed skepticism about the lack of specifics in the accord struck on Friday by the two countries to work toward nuclear disarmament and a peace treaty.

They also warned that the agreement between the two Koreas would not amount to much unless the United States gave its approval at the coming meeting between President Trump and the North Korean leader, Kim Jong-un.

Others were more encouraging, suggesting that the agreement to work toward the complete denuclearization of the Korean Peninsula could be achieved in time.