On Thursday, Trump called off his planned summit with Kim, citing "tremendous anger and open hostility" revealed in statements issued by ranking North Korean diplomats.

The abrupt announcement came hours after North Korea demolished its Punggye-ri nuclear test site in a northeastern mountainous area in front of international journalists.

In response, North Korea's Vice Foreign Minister Kim Kye-gwan said Friday that his country is still willing to talk with the United States to resolve pending issues "anytime and in any format."

Meanwhile, the main opposition Liberty Korea Party expressed regret over Trump's decision, while stressing the need to keep pressure and sanctions on the North.

"My party has consistently hoped that the US-North Korea summit could lead to the North's complete denuclearization and permanent peace on the peninsula. But it is very regrettable that the move falls through," party chief Hong Joon-pyo said on his Facebook account.

He called for more prudence in dealing with the North, stressing that Seoul and Washington should strengthen their alliance to put pressure on the North to give up nuclear weapons.

The minor opposition Party for Democracy and Peace said it will ask a parliamentary speaker to consider sending a delegation of lawmakers to the US over the cancellation of the US-North Korea summit.

"It is not appropriate for Trump to release an open letter for the summit cancellation, but hopes for negotiations do not falter," Chung Dong-young, a lawmaker of the opposition party, said.

"President Moon Jae-in needs to communicate with Trump and talk with Kim over a hotline to help bring a dramatic turnaround to the current situation (as a mediator)," he added.

South and North Korea set up a telephone hotline between their leaders last month ahead of their summit on April 27, but President Moon Jae-in and Kim Jong-un have yet to use it. (Yonhap)