The US has forward deployed a specialist missile reconnaissance aircraft to Japan, apparently out of concern that North Korea is preparing to launch a rocket.

The US Air Force RC-135S aircraft - known as a Cobra Ball - arrived at Kadena Air Base in Okinawa on Saturday evening, the JoongAng newspaper reported on Monday. It flew to Japan from the Indian Ocean base of Diego Garcia after monitoring an anti-satellite missile test conducted by the Indian military.

The US Air Force operates three of the spy aircraft, which were rotated through the Kadena base in 2017, when North Korea tested more than a dozen missiles with varying ranges over a period of several months. The aircraft use radar, infrared and visible spectrum cameras to track ballistic missiles in flight.

The arrival of the aircraft in Japan comes just days after South Korea’s intelligence agency reported to members of parliament in Seoul that the North is close to completing work to renovate and restore its Sohae Satellite Launching Station.

Work to disassemble facilities at the site began in July 2018, just weeks after Kim Jong-un, the North Korean leader, met with President Donald Trump in Singapore.