"Kim Jong Un inspected the testing of a newly developed high-tech tactical weapon at the Academy of National Defence Science," Yonhap cited the North's state broadcaster as saying.

It said the test was successful but did not specify the type of device involved.

The "high-tech tactical weapon" had been developed over a long period and "builds impregnable defences of our country and strengthens the fighting power of our people's army", it added.

Pyongyang's suspension of nuclear weapon and ballistic missile tests has been key to this year's rapid diplomatic developments and North Korean-US negotiations, and has been repeatedly praised by President Donald Trump.

Trump and Kim met in a historic summit in Singapore in June, where they signed a vaguely-worded document on denuclearisation of the peninsula.

Progress has since stalled as Washington and Pyongyang spar over the meaning of the document, and a return to testing would cast grave doubts over the future of the process.

"That pit of dread you felt in your stomach when you read this is your reminder that the DPRK missile test pause is voluntary, partial, and can fail without notice if it isn't explicitly codified," Adam Mount of the Federation of American Scientists tweeted in response to the report, using the country's official acronym.