President Donald Trump on Thursday canceled a scheduled June 12 summit in Singapore with North Korean leader Kim Jong Un after recent sparring between the two countries over the planned nuclear talks.

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 wrote in a letter to Kim, which was sent to reporters.

Read Trumps letter (story continues below):

South Korean officials appeared blindsided by the announcement.

We are attempting to make sense of what, precisely, President Trump means, said spokesman Kim Eui-kyeom, according to The Washington Posts Anna Fifield .

South Korean President Moon Jae-In urged both Trump and Kim to hold direct talks, South Koreas Yonhap News Agency reported .

Its also unclear whether State Department officials were aware of Trumps decision before he released the letter. When asked if the announcement came as a surprise, a staffer in the office that works on North Korea issues said he had to check with State Department spokeswoman Heather Nauert.

Speaking at the White House later Thursday, Trump said he had just spoken with military officials, as well as the leaders of South Korea and Japan. They are ready for foolish or reckless acts be taken by North Korea, he said, adding that an unfortunate situation is forced upon us.

Hopefully positive things will be taking place with respect to the future of North Korea. If they dont, we are more ready than we have ever been before, he said, apparently a threat of military action.

On a call with reporters, a senior White House official asserted that Trump had constant communication with our allies, but did not explain why U.S. allies were caught off guard. The official did not say whether Trump and Kim had spoken directly.

Of the letter, the official said Trump had dictated every word himself.

Trumps announcement came hours after North Korean officials threatened to cancel the summit , angered by recent comments from Vice President Mike Pence and national security adviser John Bolton, who compared North Korea with Libya.