SEOUL - US President Donald Trump and South Korean President Moon Jae-in on Sunday discussed North Korea’s recent threats to cancel its unprecedented summit with Washington, Seoul’s presidential office said.

After weeks of warm words and diplomatic backslapping, Pyongyang abruptly threatened to pull out of the planned summit next month because of US demands for “unilateral nuclear abandonment”, according to the North’s official KCNA news agency. North Korea also cancelled at the last minute a high-level meeting with the South, protesting joint military drills between Seoul and Washington.

In a phone conversation on Sunday, Trump and Moon “exchanged views on various actions taken by North Korea recently”, Moon’s office said in a statement.

The two leaders agreed to “work closely” for the success of the landmark summit in Singapore on June 12, which would be the first meeting between a sitting US President and a North Korean leader. They are due to meet in Washington on Tuesday.

North Korea’s sudden shift in attitude followed a weeks-long charm offensive that has seen leader Kim Jong Un hold a historic summit with Moon and meet twice with Chinese President Xi Jinping. At a dramatic summit last month in the Demilitarised Zone dividing their two countries, Kim and Moon pledged to pursue nuclear disarmament and a peace treaty. Pyongyang also raised hopes ahead of the US summit by announcing it will destroy its nuclear testing site next week.

But the promise is open to interpretation on both sides and the North has spent decades developing its atomic arsenal, culminating last year in its sixth nuclear test - by far its biggest to date - and the launch of missiles capable of reaching the US.

Pyongyang demands Seoul return waitress ‘defectors’

North Korea has demanded Seoul repatriate a dozen waitresses who fled to the South two years ago, just days after abruptly calling off a planned inter-Korean meeting following weeks of tentative rapprochement. The issue has long been controversial, with Pyongyang claiming the women were kidnapped from a North Korean state-run restaurant in China while Seoul insists they defected of their own free will.

But the restaurant’s manager said in a recent interview he had lied to the women and blackmailed them into following him under the orders of the South’s spy agency.

The fate of the women could jeopardise relations between the two countries, said a statement from the North’s Red Cross carried by the official KCNA news agency late Saturday.

“The South Korean authorities should... send our women citizens to their families without delay and thus show the will to improve North-South ties,” the statement said.

At a landmark summit last month in the Demilitarised Zone that divides the peninsula, North Korean leader Kim Jong Un and the South’s President Moon Jae-in pledged to pursue denuclearisation and a peace treaty.

A rapid thaw in tensions earlier this year saw Pyongyang release three US detainees and invite foreign media to witness the closing of its nuclear test site ahead of a planned summit between Kim and President Donald Trump in Singpore next month.

But Pyongyang “indefinitely” postponed a high-level meeting with the South last week in protest of joint military exercises between Seoul and Washington and also has threatened to cancel the Singapore summit.