US President Donald Trump today called off his planned June 12 summit meeting with North Korean leader Kim Jong Un in a letter released by the White House, even after North Korea followed through on a pledge to blow up tunnels at its nuclear test site.

- North Korea blows up nuclear test tunnels 

- Follows through on pledge made about a month ago 

- North Korean vice minister calls Pence "political dummy" 

​- China hopes summit can go ahead

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Referring to a scheduled June 12 meeting with Kim in Singapore, Trump said in a letter to the North Korean leader: "I was very much looking forward to being there with you. Sadly, based on the tremendous anger and open hostility displayed in your most recent statement, I feel it is inappropriate, at this time, to have this long-planned meeting."

Trump called it "a missed opportunity" and said someday he still hoped to meet Kim.

Earlier today, North Korea repeated a threat to pull out of the unprecedented summit with Trump next month and warned it was prepared for a nuclear showdown with Washington if necessary.

In a statement released by North Korean media, Vice Foreign Minister Choe Son Hui had called US Vice President Mike Pence a "political dummy" for comparing North Korea - a "nuclear weapons state" - to Libya, where Muammar Gaddafi gave up his unfinished nuclear development programme, only to be later killed by NATO-backed fighters.

A small group of international media selected by North Korea witnessed the demolition of tunnels at the Punggye-ri site on Thursday, which Pyongyang says is proof of its commitment to end nuclear testing.

The apparent destruction of what North Korea says is its only nuclear test site has been widely welcomed as a positive, if largely symbolic, step toward resolving tension over its weapons. North Korean leader Kim has declared his nuclear force complete, amid speculation the site was obsolete anyway.