Image copyright AFP Image caption The two leaders met three times in 2018, twice at the border and once in Pyongyang

North Korea's leader Kim Jong-un has vowed to "frequently" meet South Korea's President Moon Jae-in next year to discuss denuclearisation.

In a rare letter to Seoul, Mr Kim said he wished to pursue peace between the countries and "solve the issue of denuclearising the peninsula together", a spokesman for Mr Moon said.

Mr Kim also expressed "much regret" that he could not visit Seoul in 2018.

He promised to make the trip after Mr Moon visited Pyongyang in September.

On his visit to North Korea's capital, Mr Moon gave a speech at the Mass Games, saying the two countries should "become one" again.

Although both countries technically remain at war, relations improved markedly in 2018 thanks to a number of conciliatory gestures from Mr Kim.

Mr Moon's spokesman did not reveal how the letter was delivered, but described it as warm and said Mr Kim wrote of his "strong determination to visit Seoul while watching the future situation".

Kim Jong-un also met US President Donald Trump in 2018 - the first time a sitting US president has met a leader from the country - but efforts to improve relations between the US and the north have stalled in recent months.

Image copyright AFP/Getty Image caption President Trump met Mr Kim at a historic summit in Singapore

The US has said North Korea has not fully committed to giving up its nuclear weapons, while the North has lashed out at fresh US sanctions crippling its economy and targeting members of its government.

Despite these setbacks, another summit between Mr Trump and Mr Kim could happen in 2019.

The US president praised a "warm letter" from Pyongyang in September, although no date has been set for another meeting.