WASHINGTON -- US President Donald Trump should focus on ways to denuclearize North Korea when he meets with Kim Jong-un, before addressing other issues, such as human rights, a former US ambassador to South Korea said Tuesday.

"If it were me, I would be on the denuclearization track," Mark Lippert, Washington's top envoy to Seoul from 2014-2017, said at the US Institute of Peace. "It's the most, I think, dangerous. It's the most imminent in terms of just how big the (nuclear) program is."

Trump and Kim are expected to meet by early June after the regime raised tensions last year with its sixth nuclear weapons test and multiple tests of missiles capable of striking the mainland US.

Lippert acknowledged that the question of North Korea's human rights abuses and missile technology should also be addressed.

"But I would probably put denuclearization at the top of the pile. I'd focus directly on that," he said. "That's where the international community's sanctions effort's concern is. Making progress on that is critical."