Pyongyang, May 1 (IANS): North Korea's nuclear test site is fully operational, despite Pyongyang's announcement last month that it would shut down the facility, a specialised website said in a report on Tuesday.

Pyongyang offered to permanently close down the Punggye-ri nuclear test site in the presence of international observers and journalists after the two Koreas agreed on a complete denuclearisation of the Peninsula during the April 27 historical summit between South Korean President Moon Jae-in and North Korean leader Kim Jong-un, reports Efe news.

"The two mountainous areas accessible by the South and West Portals remain viable, and could support future underground nuclear testing," the website 38 North said in its report after analysing new radar data about the site.

The report also confirms that the two central tunnels of the site were in good condition, contrary to earlier reports by experts which said they could have been irreversibly damaged after the sixth and most powerful underground nuclear test carried out by Pyongyang in September.

The report also confirms Kim's earlier assertion that Pyongyang was shutting down not defunct but rather operational nuclear facilities, including the Punggye-ri nuclear test site, the centre where it carried out all of its six nuclear tests.

During the summit, Kim had proposed that the Punggye-ri site should be shut down publicly to highlight Pyongyang's commitment to denuclearization.

The website said that although the north portal - used by Pyongyang for five of the six tests - seems to have been abandoned, they detected construction of new tunnels in another section of the test site.

It is linked to the John Hopkins University in the US - said that the new tunnels could allow the use of underground installations, dismissing analysis by other experts which said North Korea had announced the closure of Punggye-ri because the facility had become completely unusable.