The operation came in the first administration of President Donald Trump during sensitive nuclear talks with Kim, whom the US leader met three times.

The mission was considered so risky that it required direct presidential approval, the Times said, but Trump insisted Friday he had no knowledge of the operation.

"I don't know anything about it. I'm hearing it now for the first time," the president told journalists.

Despite months of practice, the mission still went horribly wrong, the Times reported.

The SEALs -- from the same unit that killed Osama bin Ladin in 2011 -- approached North Korea in mini-submarines that exposed them to frigid water for hours, then swam ashore, according to the newspaper, which interviewed two dozen people to piece together the account.

The special forces personnel thought they were alone, but didn't see a small boat in the area.

The boat later approached the mini-subs, with the crew carrying flashlights. One person jumped into the water.

Thinking the mission was compromised, the senior enlisted SEAL ashore opened fire on the boat, as did the others with him.

When they reached the boat, they found two or three bodies, but no guns or uniforms: the dead were apparently civilians who were diving for shellfish.

The SEALs used knives to puncture the lungs of the boat's crew so the bodies would sink, and were able to escape unharmed.

The Times said the operation prompted a series of military reviews that found the killings were justified.

The results of the reviews were classified, and key congressional leaders were kept in the dark.

While the failed mission did not create a major international crisis, it easily could have, and the incident highlights both the impunity and secrecy under which America's elite forces operate around the globe.