Singapore Prime Minister Lee Hsien Loong says he has outlined for President Donald Trump his country's efforts to pressure North Korea over its nuclear program but also advised the US leader to use talks to help resolve the conflict.

"Pressure is necessary, but so is dialogue," Lee said in remarks with Trump at the White House on Monday. "The US will need to work with others, including China, South Korea and Japan and Russia, to resolve the issue."

He urged Trump to build a good relationship with China, noting that Singapore and other countries in the region "watch your relations with China very closely" and see it as "the most important bilateral relationship in the world".

It comes after an official said Trump will press Chinese President Xi Jinping during a visit to Beijing next month to do more to rein in North Korea.

Trump will urge China to fully implement the UN Security Council's sanctions resolutions against Pyongyang and to take bilateral steps that go beyond that, the official told reporters ahead of Trump's Asia trip.

The failure to confront and reverse the nuclear and missile threat from North Korea will lead to a "much darker era", the official said on Monday, speaking on condition of anonymity.

But the official also said Trump is looking for a peaceful resolution of the North Korea standoff.