SEOUL - North Korea is demanding that the U.S. "do everything" before Pyongyang makes any concessions, Harry Harris, the U.S. Ambassador to South Korea, said in an interview published Monday.

Harris' comments to South Korea's Dong-A-Ilbo newspaper are the first substantive reaction by a U.S. official since North Korea walked away from working-level nuclear talks late last week and blamed the U.S. for the breakdown.

While noting he was not present at the negotiations held in the capital of Sweden, Harris suggested that North Korea, not the U.S., was to blame for the impasse.

"In my view, North Korea demanded that the United States do everything before doing anything," Harris was quoted as saying. He did not elaborate.

The U.S. State Department previously insisted the discussions went "good," and pushed back against North Korea's accusation that U.S. negotiators failed to bring any new ideas to the talks.

North Korea has since threatened to resume long-range ballistic missile or nuclear tests and reiterated its end-of-year deadline for the U.S. to take a more flexible approach.

In the interview, conducted Friday, Harris downplayed the importance of the deadline, calling it "artificially set" by North Korea.

"The U.S. still wants to keep up the dialogue" and figure out how to implement the declaration signed by U.S. President Donald Trump and North Korean leader Kim Jong Un in Singapore in June 2018, Harris said. But whether that happens "depends on North Korea," he added.

Trump has met Kim two other times since Singapore, and has recently said he is open to a fourth meeting.

But Trump has not set a timeline for such a summit, Harris said, adding: "We think it is better to have serious working level talks."

"(Harris) also said yes when asked if his comment means that Washington would not pursue a summit with the North before they see progress in working-level talks," the report noted.

Talks have been stalled since February, when Trump walked away abruptly from a meeting with Kim in Hanoi, Vietnam. At that meeting, Trump rejected Kim's offer to dismantle a key nuclear facility in exchange for lifting a majority of sanctions against Pyongyang.

U.S. and North Korean officials have not commented on what either side offered in Stockholm.

North Korea's foreign ministry insisted last week the North would not hold any more "sickening negotiations" until the U.S. takes a "substantial step" toward a "complete and irreversible withdrawal" of its "hostile policy."

Trump has not publicly reacted to the latest breakdown in talks. But in recent months, Trump has given several signs he is more interested in reaching a deal.

Trump recently fired John Bolton, his national security advisor, who disagrees with the White House's outreach to Kim. Trump has also spoken of the need for a "new method" to the nuclear talks.