SEOUL, South Korea (AP) — North Korea on Sunday said it's running out of patience with the United States over what it described as hostile policies and unilateral disarmament demands, and warned that a close personal relationship between the leaders alone wouldn't be enough to prevent nuclear diplomacy from derailing.

In a statement published by Pyongyang's official Korean Central News Agency, senior North Korean official Kim Yong Chol said there has been no substantial progress in relations despite warm ties between leader Kim Jong Un and President Donald Trump. He said the persisting hostility means "there can be the exchange of fire at any moment."

Kim Yong Chol said the Trump administration would be "seriously mistaken" if it ignores an end-of-year deadline set by Kim Jong Un to propose mutually acceptable terms for a deal to salvage nuclear negotiations.

The North issued a similar statement on Thursday that was attributed to veteran diplomat Kim Kye Gwan. He criticized U.S. officials for maintaining "Cold War mentality and ideological prejudice" and urged the United States to act "wisely" through the end of the year.

"My hope is that the diplomatic adage that there is neither permanent foe nor permanent friend does not change into the one that there is a permanent foe but no permanent friend," Kim Yong Chol said, stressing that the United States would fail if it tries to use the "close personal relations" between Trump and Kim for delaying tactics.