North Korea severs last tie with US

North Korea said Monday that it had cut off its only official channel of diplomatic communications with the United States in retaliation for Washington's sanctions against its leader, Kim Jong-un, over human rights abuses.

The North's diplomatic mission to the United Nations in New York notified the United States government of its decision on Sunday to sever the channel, the North's official Korean Central News Agency said.

Although the countries have no diplomatic ties, the United Nations mission has long served as a point of contact and was often used to arrange talks aimed at ending the North's nuclear weapons program.

"Because the United States did not accept our demand that the sanctions be retracted, we are taking concrete actions one by one, the first of which is to completely cut off the New York channel of communication, the only official point of contact that has existed between the two sides," KCNA said, citing the notice.

Meanwhile, satellite imagery indicates a high-level of activity at North Korea's nuclear test site to ensure the facility is always ready for use on any orders from Pyongyang, a US think-tank said.

The US-Korea Institute at Johns Hopkins University said images from July 7 of the Punggye-ri site show what appear to be supplies and/or equipment stacked next to the North Portal where the North conducted its fourth nuclear test in January, reports AFP.

"Based on imagery alone, it is not possible to determine whether this activity is for maintenance, excavation or preparation for a fifth nuclear test", it said Monday on its website 38 North.

"Nevertheless, it is clear that North Korea is ensuring that the facility is in a state of readiness that would allow the conduct of future nuclear tests should the order come from Pyongyang," it added.

Tensions are high since Pyongyang carried out its fourth nuclear test in January, followed by a series of missile launches.