South Korea’s new President Moon Jae-In and US President Donald Trump agreed Wednesday on “close cooperation” in dealing with North Korea’s nuclear weapons program, Seoul’s presidential office said.

In their first phone call since Moon’s inauguration, the two leaders “agreed on close cooperation in resolving security concerns on the Korean peninsula including North Korea’s nuclear ambitions,” the Blue House said in a statement.

Calling Pyongyang’s atomic weapons program a “a difficult problem that can be solved”, Trump invited Moon to visit the United States “as early as possible”, according to the statement.

Moon was sworn in Wednesday, just a day after a landslide election victory following the ouster of his predecessor Park Geun-Hye over a massive corruption scandal.

Moon backs engagement with the nuclear-armed North in the quest for peace — in contrast to the threatening rhetoric from the Trump administration in recent weeks — and has immediately declared his willingness to visit Pyongyang.

“If needed I will fly to Washington immediately,” Moon said in an inauguration speech after taking the oath of office in front of lawmakers at Seoul’s National Assembly building.

“I will also go to Beijing and Tokyo and even Pyongyang in the right circumstances.”

But Trump recently appeared to offer the prospect of a diplomatic off-ramp last week, saying he would be “honored” to meet North Korean leader Kim Jong-Un under the right conditions.