South Korea's nuclear envoy visits US as tensions flare with North Korea

South Korea's chief nuclear negotiator will hold talks with officials in Washington on Thursday amid flaring tensions with North Korea after Pyongyang blew up an inter-Korean liaison office and threatened military action.

Lee Do-hoon's unannounced trip came days after North Korea blew up a joint liaison office in Kaesong, near the South Korean border and declared an end to dialogue with the South.

Lee is expected to hold consultations with U.S. officials, including Deputy Secretary of State Stephen Biegun who had led denuclearisation negotiations with North Korea, Seoul's foreign ministry said.

Lee and Biegun will "assess the current situation on the Korean peninsula and discuss responses," the ministry said in a statement.

South Korean television showed Lee arriving at Washington's Dulles International Airport on Wednesday evening, where he declined to comment to reporters.

Pyongyang has increasingly snubbed Seoul's calls for engagement as efforts to restart inter-Korean economic projects stalled due to international sanctions designed to rein in the North's nuclear and missile programmes.

North Korean leader Kim Jong Un's sister, Kim Yo Jong, on Wednesday criticised South Korean President Moon Jae-in for failing to implement a 2018 peace accord, saying Moon "put his neck into the noose of pro-U.S. flunkeyism."

Pyongyang has also taken issue over defectors in the South sending propaganda leaflets into North Korea.

Several defector-led groups regularly send back flyers carrying critical messages of Kim Jong Un, often together with food, $1 bills, mini radios and USB sticks containing South Korean dramas and news.

The Rodong Sinmun, the official newspaper of the North's ruling Workers' Party, said the demolition of the liaison office was the "first stage action" in its "holy war" aimed at punishing Seoul authorities for turning a blind eye to the defector's campaign.

"It was an iron hammer of stern punishment meted out to those who were having empty dreams while pursuing concealed hostile policy," it said in a commentary.

The newspaper also ran a series of articles and photos carrying angry ordinary citizens calling for retaliation and vowing to send anti-South leaflets over the border.