Nuclear-armed North Korea on Monday warned it could cut off dialogue with the United States, but Washington's top diplomat said the US still looked forward to talks, even after the North called his insistence on sanctions "ludicrous".

Secretary of State Mike Pompeo last week told nations to "stay committed to applying diplomatic and economic pressure" over the North's nuclear and ballistic missile programmes while calling on it to return to talks.

A string of weapons drills by Pyongyang has come during a prolonged hiatus in disarmament talks with the US and despite overtures from Washington offering help against the coronavirus pandemic.

"Listening to Pompeo's ludicrous language made us give up on any hopes for dialogue," an unnamed official in charge of negotiations with the US said in a statement released by the North's official Korean Central News Agency.

"We will walk our way," the official said.

Analysts say the North continues to refine its weapons capabilities more than a year after a summit between the North's leader Kim Jong Un and President Donald Trump broke down in Vietnam.

Negotiations have since been deadlocked over sanctions relief and what the North would be willing to give up in return.

North Korea is under multiple sets of sanctions from the United Nations, United States and others over its banned weapons programmes.

Pompeo had "unleashed insult at a country with which his president was willing to forge a good relationship", the official continued, referring to Trump's letter sent to Kim expressing an intent to cooperate in anti-epidemic efforts.

"It is puzzling who the real commander in chief is in the US," the official said.

Waiting for 'progress'

But in a telephone briefing with South Korea's Yonhap and other Asian news outlets, Pompeo said his position and that of Trump have always been "in lockstep."

"We have been trying very diligently from the American side since to move forward with those negotiations and hope that we will get an opportunity to do that," Pompeo said, referring back to the groundbreaking 2018 summit in Singapore between Trump and Kim.

At that meeting, the two men signed a vague statement on denuclearisation.

"President Trump has also been clear, until we get to that point, till we get to the point where we have made sufficient progress along the way, the sanctions -- not American sanctions, but UN Security Council resolutions -- will continue to be enforced and in place," Pompeo added.

The criticism from the North Korean official came after the North earlier Monday said it had successfully tested "super-large multiple rocket launchers" the day before.

South Korea said two projectiles -- presumed to be ballistic missiles -- were fired on Sunday from the North Korean port city of Wonsan into the Sea of Japan, also known as the East Sea.

With the world focused on the coronavirus pandemic, the isolated state has carried out four such firings this month.

Unusually, KCNA did not say in its report on the rocket launchers that Kim had directed Sunday's test. Analysts said the North is seeking to normalise such events.

Pompeo told Yonhap that the US stands by its offer to help North Korea fight the new coronavirus.

He added that he hoped the North, and Iran, would be transparent in their reporting of cases, fatalities, and their efforts to reduce the spread so that effective global counter-measures can be developed.

North Korea is one of the few remaining countries in the world yet to report a case of novel coronavirus infection. But there has been widespread speculation that the virus has reached the isolated and impoverished nation.