Pyongyang wants to know if US President Donald Trump is “crazy”, according to a senior US academic who has held secret back channel talks with North Korean officials four times over the past year.

“They want to know if he’s crazy…or if this is just an act,” Suzanne DiMaggio, a director at the New America think tank told Politico in an interview.

In meetings spanning Geneva, Pyongyang, Oslo and Moscow, North Koreans have focused on the president’s “erratic behaviour,” she said. “They really want to know what his end game is.”

They have raised Mr Trump’s domestic troubles, including the investigation into possible campaign collusion with Russia and its potential threat to his presidency, and questioned Mr Trump’s undercutting of his Secretary of State Rex Tillerson, asking if it is a game of “good cop, bad cop”.

For years Ms DiMaggio, who specialises in talking with rogue regimes, and Joel Wit, a former US diplomat who founded the influential North Korea-monitoring website 38North, have been quietly meeting the North Koreans to talk about their nuclear programme.