TOKYO -- North Korean leader Kim Jong Un complained of "U.S. hegemonism" to Russia's visiting foreign minister on Thursday, a comment likely to complicate ties with the United States as plans proceed for Kim's expected summit with President Trump in Singapore next month. Kim told Sergey Lavrov that he hopes to boost cooperation with Russia, which has remained largely on the sidelines in recent months as Kim has made a major diplomatic outreach to the United States as well as to South Korea and China.

"As we move to adjust to the political situation in the face of U.S. hegemonism, I am willing to exchange detailed and in-depth opinions with your leadership and hope to do so moving forward," Kim told Lavrov.

Kim has previously made harsher comments and even threatened to launch nuclear attacks on the United States numerous times. But his comments Thursday come at a sensitive moment, when one of his top lieutenants is in New York for talks with Secretary of State Mike Pompeo on the planned summit.

Since January, Kim has significantly toned down his rhetoric against Washington and Seoul and tried to reach out to them following a year of heightened nuclear tensions that saw increased fears of war on the Korean Peninsula.

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Kim has indicated he is willing to relinquish his nuclear arsenal in exchange for security guarantees from the United States. But continuing differences between the two countries led Mr. Trump to abruptly cancel the planned summit last week, and then quickly announce that it might still be held as scheduled on June 12.

Despite having a border with North Korea and relatively cordial relations that Putin has seemed to want to develop further, Russia has kept a surprisingly low profile as Kim has emerged onto the world stage this year, meeting twice with Chinese President Xi Jinping and South Korean President Moon Jae-in.

Lavrov's visit to Pyongyang suggests that Russia wants to become involved and make sure North Korea informs it of its intentions and is mindful of Moscow's concerns.

In their talks, Lavrov relayed President Vladimir Putin's "warmest regards and best wishes" for Kim's "big endeavors" on the Korean Peninsula. He also expressed Moscow's support for an agreement Kim reached with Moon at a summit last month that focused on measures to ease hostilities and increase exchanges between the two Koreas.

Video of the beginning of their meeting also showed Lavrov inviting Kim to Moscow.

According to Russian media, he also discussed ways to expand relations during a meeting with Foreign Minister Ri Yong Ho.

"We welcome the contacts that have been developing in the recent months between North and South Korea, between North Korea and the United States," Lavrov said in comments to the media. "We welcome the summits that already took place between Pyongyang and Seoul as well as planned meetings between North Korean and U.S. leadership."

He vowed Russia's support for denuclearization and a broader effort to create a stable and long-lasting peace in the region, but indicated that Moscow believes sanctions can be eased while the process is in progress, which diverges from the U.S. position that denuclearization must come first.

"It's absolutely obvious that when a conversation starts about solving the nuclear problem and other problems of the Korean Peninsula, we proceed from the fact that the decision can't be complete while sanctions are still in place," he said.

That means that North Korea has Russia, China and South Korea on its side versus the U.S, which is now one of the only powers arguing that sanctions relief should come later, CBS News' Margaret Brennan reports. Kim Jong Un seems to be triangulating and splitting the pressure campaign.

As Lavrov was visiting Pyongyang, former North Korean intelligence chief Kim Yong Chol was in New York to discuss the agenda for the Trump summit with U.S. officials.