North Korea is reported to be developing an advanced version of its intercontinental ballistic missile (ICBM) that could potentially reach the mainland United States.

A US official told CNN that an upgraded version of Pyongyang’s existing KN-20 is part of an accelerated effort by dictator Kim Jong-un’s regime to improve its nuclear and missile capabilities.

The revelation comes less than six months after North Korea tested its first ICBM and triggered its sixth underground nuclear test.