Boris Johnson will urge Donald Trump not to withdraw the US from the 2015 Iran nuclear deal, arguing that similar "diplomatic imagination" could resolve the crisis on the Korean Peninsula.

The foreign secretary's intervention will come a week after Trump decertified the landmark agreement claiming it was not in the US national interest, and threatened to withdraw from the pact altogether.

Johnson, who is to deliver his remarks at Chatham House in London on Monday, will praise Secretary of State Rex Tillerson for keeping diplomatic options open with Pyongyang, despite Trump dismissing talk with the regime as a "waste of time."

Heralding the "astonishing" and "extraordinary" 1970 nuclear non-proliferation treaty, Johnson will say that "far-sightedness is now needed more than ever, not only to keep the NPT, but also one of its most valuable complementary accords, the nuclear deal with Iran."

On North Korea, Johnson will push for a policy of "toughness but engagement."

"It is right that Rex Tillerson has specifically opened the door to dialogue," Johnson will say. "This is the moment for North Korea's regime to change course - and if they do the world can show that it is once again capable of the diplomatic imagination that produced the nuclear non-proliferation treaty - arduously negotiated - and that after 12 years of continuous effort produced the JCPOA nuclear deal with Iran."

Warning of the consequences diplomatic failure, the foreign secretary will highlight how a "new generation has grown up with no memory of the threat of a nuclear winter, and little education in the appalling logic of mutually assured destruction."

"The NPT is one of the great diplomatic achievements of the last century," her will say. "It has stood the test of time. In its restraint and its maturity it shows an unexpected wisdom on the part of humanity, and almost evolutionary instinct for the survival of the species.

"It is the job of our generation to preserve that agreement, and British diplomacy will be at the forefront of the endeavour."