North Korea is known to have increased security around a site where it conducted a nuclear test last year.

The Seoul-based Yonhap News Agency quoted Sunday a Seoul official as saying intelligence has shown that guards and additional fencing have been put at the nuclear test site at Gilju, North Hamkyong Province.

The report said South Korean and U.S. authorities are keeping a close watch on the area and analyzing the North’s intentions.

The official said Pyongyang authorities seem to be strictly restricting access to the site, but did not consider the situation serious.