North Korea vowed Friday to build up a "more reliable" force against military threats from the United States, saying the historic summit two years ago between leader Kim Jong-un and US President Donald Trump led to no improvement in relations between the two countries.

North Korean Foreign Minister Ri Son-gwon made the remark, adding that Pyongyang would "never again" provide the US with "another package" that President Donald Trump could use to boast as his political achievements.

"The secure strategic goal of the DPRK is to build up more reliable force to cope with the long-term military threats from the US. This is our reply message to the US on the occasion of second anniversary of June 12," Ri said in a statement carried by the Korean Central News Agency.

DPRK is the acronym of the North's official name, the Democratic People's Republic of Korea.

"What stands out is that the hope for improved DPRK-US relations -- which was high in the air under the global spotlight two years ago -- has now been shifted into despair," he added.

Ri voiced frustration over a stalemate since the Singapore summit, accusing Washington of just focusing on talking up "political achievements" without taking any actual steps to fulfill agreements.

"The question is whether there will be a need to keep holding hands shaken in Singapore, as we see that there is nothing of factual improvement to be made in the DPRK-US relations simply by maintaining personal relations between our Supreme Leadership and the US President," he said.

"In retrospect, all the practices of the present US administration so far are nothing but accumulating its political achievements. Never again will we provide the US chief executive with another package to be used for achievements without receiving any returns," he added.

Ri's statement came hours after the US said that it is committed to implementing the Singapore summit agreement and is willing to take a flexible approach.

"The United States is committed to engaging the DPRK in meaningful negotiations so that North Koreans can realize a brighter future," a State Department spokesperson told Yonhap News Agency in response to a request for comment on the second anniversary of the 2018 summit between Trump and Kim.

"That offer remains on the table. We are willing to take a flexible approach to reach a balanced agreement on all of the Singapore summit commitments," the spokesperson added.

Trump and the North's leader met in Singapore on June 12, 2018, to negotiate the dismantlement of North Korea's nuclear weapons program in exchange for sanctions relief and other concessions.

The first summit between sitting leaders of the two countries produced a joint statement committing the North to "work toward complete denuclearization of the Korean Peninsula" in return for US security guarantees.

The two sides also agreed to work together to improve bilateral relations, build a lasting and stable peace regime on the peninsula, and repatriate the remains of American service members killed during the 1950-53 Korean War.

Subsequent negotiations to follow-up on the agreements, however, have stalled due to wide differences over the scope of North Korea's denuclearization and US sanctions relief, as well as the sequencing of their steps. Trump and Kim held their second summit in February last year but failed to produce an agreement.

"The US administration, through the two years of totally unjust and anachronistic practices, laid bare openly that its much-claimed improvement of relations between the DPRK and US means nothing but a regime change, security guarantee an all-out preemptive nuclear strike, and confidence building an invariable pursuit of isolation and suffocation of the DPRK," Ri said.

"All the above facts clearly prove once again that, unless the 70-plus-year deep-rooted hostile policy of the US towards the DPRK is fundamentally terminated, the US will as ever remain to be a long-term threat to our state, our system and our people," he said.

South Korea's unification ministry declined to comment on Ri's comment and the second anniversary of the Singapore summit but reaffirmed Seoul's commitment to working toward peace and prosperity on the Korean Peninsula. (Yonhap)