By Agencies

US president also says Russia has agreed to help with North Korea's pledge to dismantle its nuclear weapons programme.

US President Donald Trump has said there is no timeframe for North Korea to give up its nuclear programme.

Trump met with Chairman Kim Jong-un on June 12 in a summit that was the first of its kind between a sitting US president and a North Korean leader.

The two leaders pledged to work toward denuclearisation but stopped short of defining the process, much less ascribing a timeline for its completion.

"Discussions are ongoing and they're going very well," Trump told reporters on Tuesday, adding "we have no time limit. We have no speed limit."

Trump said he discussed North Korea with Russian President Vladimir Putin at a summit in the Finnish capital Helsinki on Monday.

"President Putin is going to be involved in the sense that he is with us," Trump said.

On Wednesday, Trump reaffirmed in a tweet that Russia "had agreed to help with Noth Korea," adding sanctions he extended on Pyongyang earlier in April would remain in place.

....Russia has agreed to help with North Korea, where relationships with us are very good and the process is moving along. There is no rush, the sanctions remain! Big benefits and exciting future for North Korea at end of process!

— Donald J. Trump (@realDonaldTrump) July 18, 2018

Earlier in June, US broadcaster NBC News reported that US intelligence agencies believed North Korea continued producing fuel for its nuclear programme.

It said the intelligence community believes the weapon is deemed essential by the communist state for its survival as it positions "itself to extract every concession it can from the Trump administration".

Secretary of State Mike Pompeo's announcement that progress had been made "on almost all of the central issues" in ministerial-level talks held in July, including on setting a timeline for Pyongyang's denuclearization was met with rebuke by North Korean officials.

"We had expected that the US side would offer constructive measures that would help build trust based on the spirit of the leaders' summit.

"We were also thinking about providing reciprocal measures," an unnamed spokesperson of North Korea's foreign ministry said at the time in a statement published by the official Korean Central News Agency.

"However, the attitude and stance the United States showed in the first high-level meeting [between the countries] was no doubt regrettable," the spokesperson added.