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.