U.S. Secretary of State Rex Tillerson (L) shakes hands with Chinese President Xi Jinping (R) before their meeting at the Great Hall of the People on September 30, 2017 in Beijing, China.

The US is in “direct contact” with North Korea, Secretary of State Rex Tillerson has said.

Mr Tillerson said Washington was “probing” the possibility of talks with Pyongyang, “so stay tuned”.

“We have lines of communications to Pyongyang,” he said during a trip to China. “We’re not in a dark situation.”

North Korea and the US have engaged in heated rhetoric in recent months but it was not previously known they had lines of communication.

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US President Donald Trump has threatened to annihilate North Korea, saying the country’s leader, Kim Jong-un, “is on a suicide mission”, which led Mr Kim to release a statement vowing to “tame the mentally deranged US dotard with fire”.

North Korea continued the rhetoric into Saturday, releasing a statement calling Mr Trump an “old psychopath” bent on the “suicidal act of inviting a nuclear disaster that will reduce America to a sea of flames”.

The war of words comes against a backdrop of repeated missile tests and Pyongyang’s claim that, on 3 September, it successfully tested a miniaturised hydrogen bomb which could be loaded on to a long-range missile.

Media captionNorth Koreans rally against “dotard psycho Trump”

The tests were internationally condemned, with the UN bringing in sanctions against North Korea in an attempt to force the secretive state to stop its weapons programme.

Mr Tillerson is in China meeting with President Xi Jinping and other officials, hoping to encourage them to implement the sanctions.

China this week told North Korean businesses operating in its territory to close down. However, China remains keen to see negotiations with North Korea.

Mr Trump said last month that “talking is not the answer”.

But there were reports of so-called back channels between the two administrations.

According to the news agency¬†Associated Press, the countries had been engaged in quiet discussions for months, with “diplomatic contact… occurring regularly” between the US envoy for North Korea policy and “a senior North Korean diplomat at the country’s UN mission”.

Media captionTrump: ‘Rocket Man’s suicide mission’

Mr Tillerson has also previously hinted there are channels available between the two countries, AP added.

More widely known is the role Sweden plays in negotiating with North Korea on Washington’s behalf.

In August, Ulv Hanssen from the Swedish Institute of International Affairs told Reuters news agency Sweden could step in again because it was trusted by both Washington and Pyongyang.

“Sweden has done so on numerous occasions before, especially in relation to imprisoned Americans,” he said.

The Swedish Foreign Ministry declined to comment on the speculation.