A former US envoy for North Korea said Monday that Pyongyang's recent test of a submarine-launched ballistic missile ruined its chances of reaching a nuclear deal with Washington in Sweden earlier this month.

Joseph Yun, who served as US special representative for North Korea policy until early last year, spoke at a forum after fresh working-level denuclearization negotiations between the United States and North Korea broke down in Stockholm on Oct. 5.

The talks had resumed for the first time since the collapse of February's second summit between US President Donald Trump and North Korean leader Kim Jong-un, but the North Koreans walked away, blaming the US for failing to come up with a new proposal.

Yun said launching an SLBM just three days before the meetings was one of two "mistakes" North Korea made ahead of the negotiations.

"The US delegation is going there because the US side has asked publicly many, many times for the meeting," the former envoy said at the seminar hosted by the George Washington University's Institute for Korean Studies.

"To go there was bad enough ... after they've done a show of force in terms of the SLBM launch," he said. "But to go there, then come back with some weak offer, it was not going to do them any good."

North Korea's second mistake was to assume that last month's departure of hawkish former US National Security Adviser John Bolton from the Trump administration would result in the softening of Washington's demands on denuclearization, according to Yun.

"This is very typical North Korean," he said. "I think they want to take all the credit for getting John Bolton fired, but John Bolton was fired for many reasons -- probably the most important, Trump didn't like him."

Trump and Bolton clashed over Iran, the Taliban, Afghanistan and "maybe a little bit about North Korea," Yun added. "But certainly, John Bolton getting away from the scene does not mean the US position will have changed radically."

The two countries have wrangled over how much the North should dismantle its nuclear weapons and ballistic missile programs before receiving sanctions relief and security guarantees from the US.

Washington demands that Pyongyang take significant steps toward denuclearization first, while the North insists on a step-by-step process under which it would receive concessions for every denuclearization measure.

Yun suggested that an interim deal could be possible over the next six to 12 months, which would then pave the way for a third summit between Trump and Kim.

That deal, he said, could involve a North Korean offer to dismantle its main nuclear facility in Yongbyon, accompanied by other denuclearization measures, such as a freeze on the testing and production of nuclear material.

On the US side, it could involve limited sanctions relief, humanitarian assistance and a political declaration ending the 1950-53 Korean War, among other measures.

In the meantime, Yun suggested that Trump would be OK with the status quo as long as North Korea does not cross two "red lines" -- nuclear testing and testing of intercontinental ballistic missiles.

There would be "serious consequences" for either action, he said. (Yonhap)