"Vietnam is thriving like few places on earth. North Korea would be the same, and very quickly, if it would denuclearize," Trump tweeted. "The potential is AWESOME, a great opportunity, like almost none other in history, for my friend Kim Jong Un. We will know fairly soon - Very Interesting!."

Just over a year ago the two men hurled personal insults at each other over the North's testing of nuclear weapons and ballistic missiles. Trump called Kim "Little Rocket Man," while the North Korean leader referred to the US president as a "dotard."

After their first summit in Singapore in June, Trump said the two "fell in love."

The Singapore summit produced a commitment to pursue complete denuclearization and lasting peace on the Korean Peninsula in exchange for security guarantees from the US

But critics slammed the deal as lacking in detail.

Trump has been eager to defend progress, citing the suspension of tests, the release of American prisoners and the return of the remains of American troops killed in the 1950-53 Korean War.

"The Democrats should stop talking about what I should do with North Korea and ask themselves instead why they didn't do 'it' during eight years of the Obama Administration?" he wrote in an ensuing tweet. (Yonhap)