The Scud B missiles with the range of 300 kilometres (185 miles) were loaded on a Pakistan-flagged cargo ship in North Korea's southwestern port of Nampo in mid-March, the Sankei Shimbun said.

The vessel was refuelled at a Chinese port and entered Pakistani territory in late March, it said, quoting the US official and other anonymous sources.

The United States detected the missile export with satellite information from the National Reconnaissance Office and as a result of Central Intelligence Agency espionage, it said.

The United States has slapped sanctions on a Pakistani firm and North Korea over an alleged barter deal in which it is claimed Pyongyang swapped missile components for expertise in developing a nuclear program.

Pakistan has vehemently denied the allegations.

SPACE.WIRE