The call comes after Xi met with North Korean leader Kim Jong-un in the port city of Dalian over the past two days, the second meeting between top officials of the two Communist allies in less than two months.
It is the second meeting between the two leaders in less than two months, after they held a secret meeting in the Chinese capital of Beijing in late March.
"Xi held talks with Kim and hosted a welcome banquet for him".
But after months of saber-rattling, and a historic summit between Kim and the South Korean president, Moon Jae-in, the mood is decidedly more upbeat, and Trump has said a date and location are already set - though he did not divulge any specifics. Chinese state media said Xi reiterated China's support for a U.S.
Past trips by past North Korean leaders have also followed the pattern of being carried out quietly and only discussed after they are over.
But according to reporters who were also en route with Pompeo, he said he didn't know who he'd be meeting with once he arrived.
There are no regular commercial flights between Dalian and North Korea and the airport was closed to other aircraft while the plane departed, NHK reported.
Pompeo made a secret visit to North Korea over the Easter weekend, becoming the first USA official known to have met Kim, to lay the groundwork for the planned summit.
Regional powers and the United States are seeking to prevent North Korea from obtaining nuclear weapons. He said a political resolution of tensions on the Korean Peninsula and denuclearisation should proceed in stages, with all sides moving in concert.
According to North Korean state media, Kim said he is "very pleased" with how the relationship between North Korea and China is progressing, Reuters reported Tuesday.
"With Liu coming again to Washington, it is encouraging that the two sides find something to talk about after the loggerheads visit of the Americans to China last week", Lampton told the South China Morning Post.
The young leader stirred up tensions on the Korean Peninsula with his nuclear weapons testing and purging of several key officials close to Beijing, including his uncle, Jang Song Thaek.
Kim was the first North Korean leader to touch southern soil since the end of the Korean War.
Kim was quoted as saying Monday by China's official news agency Xinhua: "I hope to build mutual trust with the US through dialogue".
The Chinese foreign ministry would not confirm or deny that a North Korean official had visited the country.