North Korea has fired missiles for the third time in eight days, which analysts say are designed to improve military capabilities and pressure the United States and South Korea as they seek to restart denuclearisation talks.

US officials, who have been hoping to revive the stalled talks with North Korea, played down the launches.

North Korea has been testing missiles despite US President Donald Trump's meeting with its leader Kim Jong-un, where they agreed to revive the talks.

The diplomatic process may have some bumps but conversations with North Korea are "going on even as we speak", US Secretary of State Mike Pompeo said in Bangkok, where he is attending a meeting of the Association of Southeast Asian Nations.

South Korea's government said the latest projectiles fired by the North appeared to be new short-range ballistic missiles.

The missiles flew 220km and reached an altitude of 25km, the Joint Chiefs of Staff in Seoul said.

A US official said US intelligence had detected at least one projectile, and possibly more, that did not pose a threat to North America.

US officials said initial information indicated they were similar to two other short-range missile tests by Pyongyang since last week.

North Korean state media said Mr Kim oversaw the firing of what it described as a new large-calibre, multiple-launch guided rocket system on Wednesday.

He also observed the launch of a short-range ballistic missile last week.

Mr Trump was asked at the White House if he thought Mr Kim was testing him and said the launches did not violate the North Korean leader's promises.

Mr Trump also said they were short-range missiles. "We never made an agreement on that. I have no problem," he said.

While Mr Trump said he never made an agreement on short-range missiles, the 15-member United Nations Security Council unanimously demanded in 2006 that North Korea suspend all activities related to its ballistic missile programme and "re-establish its pre-existing commitments to a moratorium on missile launching".

The UN Security Council met behind closed doors in New York on Thursday to discuss the latest missile launches.

Representatives from Britain, France and Germany called on North Korea after the meeting to engage in meaningful talks with the United States and said international sanctions need to be fully enforced until Pyongyang has dismantled its nuclear and ballistic missile programmes.

Representatives of the UN Security Council: Nicolas de Riviere, France, Karen Pierce, the United Kingdom, and Jurgen Schulz, Germany

Mr Pompeo said the UN sanctions remained fully in place.

"We're working with countries all across the world, many in this region, doing great work to enforce those," he said.

Mr Pompeo also said he was disappointed his North Korean counterpart had cancelled a planned trip to the  Association of Southeast Asian Nations forum.

"I think it would've given us an opportunity to have another set of conversations," he said. "I hope it won't be too long before I have a chance to do that."