US President Donald Trump on Thursday called off a planned summit with North Korean leader Kim Jong Un, even after North Korea followed through on a pledge to blow up tunnels at its nuclear test site. Referring to a scheduled June 12 meeting with Kim in Singapore, Trump said in a letter to the North Korean leader: “Sadly, based on the tremendous anger and open hostility displayed in your most recent statement, I feel it would be 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. Trumps decision came hours after North Korea said it had dismantled tunnels at its only nuclear test site. North Korea followed through on a pledge to blow up tunnels used for nuclear testing on Thursday, South Korean media reported. Reporters said they had witnessed a huge blast.at the Punggye-ri site, where North Korea has conducted all six of its nuclear tests. The site consists of tunnels dug beneath Mount Mantap in the northeast of the country. Three of its tunnels were collapsed in a series of explosions in front of about 20 handpicked international journalists. Two blasts were reportedly carried out in the morning, and four in the afternoon. The US President was looking forward to the now-canceled summit in Singapore on 12 June. "You talk about your nuclear capabilities, but ours are so massive and powerful that I pray to God they will never have to be used," he added. Trump ended his letter by saying Kim should call him if he changed his mind. Earlier on Thursday, 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 program, only to be later killed by NATO-backed fighters.