Story highlights Chinese state media says US relationship affected by "negative factors"

Speaking in Seoul, Obama described North Korea as a "hard problem"

(CNN) China's leader Xi Jinping said that ties with the US have been strained by "some negative factors" in a telephone conversation with President Donald Trump Sunday.

"Xi Jinping stressed that since his meeting with President Trump, important results have been achieved in China-US relations," reported Chinese state media outlet CCTV.

"Meanwhile, bilateral relations have also been affected by some negative factors, for which the China side has expressed its position to the US side."

JUST WATCHED Trump and China: What's at stake? Replay More Videos ... MUST WATCH Trump and China: What's at stake? 01:26

The White House statement was more reticent, saying only that the two leaders discussed a range of issues of mutual interest including North Korea and trade relations.