US President Donald Trump's hardline withdrawal from the "one-sided" Iran nuclear deal is a high-stakes gamble partly aimed at sending a muscular message to North Korean dictator Kim Jong-un ahead of their planned summit.

As Trump announced the United States was immediately quitting the Barack Obama-era international nuclear pact and reinstating the highest level of sanctions against financial transactions with oil-rich Iran, he also revealed that Secretary of State Mike Pompeo was en route to North Korea to lay the groundwork for the Kim meeting.