WASHINGTON (Yonhap) ― Mark Lippert, on track to become the new U.S. ambassador to South Korea, said Tuesday he would endeavor to help Seoul and Tokyo improve their often-prickly ties over shared history.

“We obviously have conversations to encourage better dialogue between the Japanese and South Koreans to work through some of these very difficult and painful historical issues,” he said at a Senate confirmation hearing.

Though the U.S. “wouldn’t play a mediation role,” it “can play an important role in encouraging that dialogue back and forth,”

Lippert said.

Stressing that a better relationship between Seoul and Tokyo is not only in U.S.’ national security interest but is crucial for the regional security, he remained optimistic about the ties, as both sides “are capable of making progress on the issue” based upon their shared assets such as free democracy and market economy.

Lippert, currently chief of staff to Defense Secretary Chuck Hagel, was nominated in early May to serve as the top U.S. envoy to Seoul.

He said the Pentagon has encouraged Japan to increase transparency and consultations with South Korea in pushing for the use of the right to collective self-defense aimed at broadening the nation’s military role abroad.

While the U.S. formally supports Japan’s move, South Korea, China and some other neighboring nations are concerned about it.

Lippert said the issue should be handled in a consultative manner.

In general, he said, the U.S. efforts to boost trilateral cooperation have moved forward, citing President Barack Obama’s meeting with his South Korean and Japanese counterparts in The Hague in March followed by a three-way defense ministerial talks in Singapore two weeks ago.

“I think there has been progress. But I would say that a lot more work needs to be done,” he said.

On North Korea, he said a key policy line is to continue pressure and sanctions on the nuclear-armed communist nation, while keep building the international consensus to isolate its regime.

It’s important to send a strong signal that the U.S. is not sitting back, he said.

Lippert added other top priorities for him, if confirmed, would be the full implementation of the bilateral free trade agreement, called KORUS FTA.

“There are some uneven implementation issues ― autos, origin.

The origin issue is also a big one as well that we have to continue to sort through,” he said. “I do think that the autos issue remains outstanding.”

Lippert said he has come to greatly respect the people and culture of South Korea through his many visits there.

He is also known for his expertise on Korea and broader regional security issues, having worked as assistant secretary of defense for Asian and Pacific security affairs from April 2012 to May 2013.

He is said to be among some officials who can directly telephone President Obama.