U.S. President Donald Trump will urge North Korea to act quickly to dismantle its nuclear arsenal when he meets North Korean leader Kim Jong Un and isn't willing to grant Pyongyang substantial sanctions relief in return for a freeze of its nuclear and missile tests, administration officials said.

Those two closely related questions – the pace of Pyongyang's nuclear dismantlement and the timetable for sanctions relief – stand to be the major issues of the summit, according to The Wall Street Journal.

Read also"Big progress!": Trump welcomes N. Korea's vows to stop nuclear tests

"When the president says that he will not make the mistakes of the past, that means the U.S. will not be making substantial concessions, such as lifting sanctions, until North Korea has substantially dismantled its nuclear programs," a senior Trump administration official said on Sunday.

"If North Korea is willing to move quickly to denuclearize, then the sky is the limit. All sorts of good things can happen," the official added.

Mr. Kim announced Saturday after a meeting of the central committee of North Korea's ruling party that his country would close its nuclear test site and suspend long-range missile tests. The statement has been hailed as an important move to establish a good atmosphere for a summit meeting that is expected to be held outside northeast Asia in late May or June.

Mr. Trump himself described it as "big progress" in a tweet on Friday, though in a Twitter message Sunday he added a note of caution. "We are a long way from conclusion on North Korea, maybe things will work out, and maybe they won't – only time will tell."