North Korea's Kim Yong-chol meets Mike Pompeo in Washington

One of North Korea's top negotiators is in Washington to meet US officials ahead of a possible second summit between the two countries' leaders.

Kim Yong-chol is meeting Secretary of State Mike Pompeo and could hold talks with President Donald Trump at the White House later, US media say.

He reportedly has another letter from leader Kim Jong-un to Mr Trump.

Little progress has been made on North Korean de-nuclearisation since their historic summit in Singapore last June.

Speculation is mounting that a second meeting between Mr Kim and Mr Trump could be held in Vietnam.

The North Korean leader is scheduled to travel to the communist-run country for an "official state visit" sometime in February, Reuters news agency reports, citing unnamed sources.

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There has recently been a flurry of diplomatic activity. Kim Jong-un visited China earlier this month for talks with President Xi Jinping, as he did before the Singapore summit.

Meanwhile, another senior North Korean official, vice-foreign minister Choe Son-hui, took part in talks in Sweden.

Gen Kim, a former spymaster often referred to as Kim Jong-un's right-hand man, has emerged as North Korea's lead negotiator in recent talks with the US.

He is a controversial figure and was accused of masterminding attacks on South Korean warships during his time as military intelligence chief in 2010.

He last visited Washington in June, when he delivered a letter to Mr Trump ahead of historic talks between both countries.

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It is not clear. The last time Mr Kim went to the US, his letter to Mr Trump appeared to have helped get the Singapore summit back on track.

Negotiations between both countries have stalled since then, but this meeting could be what it takes to restart talks.

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Earlier this month, Mr Trump said that the US and North Korea were negotiating over a location for another summit but US officials have not provided any further details.

The meetings in Washington could finalise plans for the summit, but just as important, analysts say, would be an understanding of what the agenda would be.

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In his annual new year's speech a few weeks ago, Mr Kim said he was committed to denuclearisation, but warned that he would change course if US sanctions remained.

Both parties signed a pledge in Singapore to denuclearise the Korean peninsula, though it was never clear what this would entail.