See the potential launch pad for North Korea's first spy satellite

North Korea will launch a spy satellite in the next 12 days, it said on Tuesday, over what it described as a need to monitor “reckless” US military exercises with neighbouring South Korea.

Satellite photos also taken on Tuesday and analysed by the Associated Press showed ongoing work at North Korea’s Sohae Satellite Launching Station.

The images from Planet Labs PBC showed the huge orange gantry – which houses a rocket on the launch pad – at the pad with its arms open. Next to the gantry, a long, rectangular object could be seen with two other objects nearby.

Those objects had not been seen in prior days’ images of the site and could potentially be rocket parts.

The reclusive nation has informed nearby Japan's coastguard that the launch would take place sometime between May 31 and June 11 and may affect waters in the Yellow Sea, East China Sea and east of the Philippines’ Luzon Island.

Japan has said it would shoot down any projectile that threatens its territory.

“Even if North Korea might call it a 'satellite', this is a violation of relevant UN Security Council resolutions that prohibit North Korea from all launches using the ballistic missile technology,” Japanese Foreign Minister Yoshimasa Hayashi told a news conference on Tuesday.

South Korea's foreign ministry also slammed the country's use of ballistic missile technology as a clear breach of UN sanctions, saying North Korea was making a “farfetched excuse” to bolster its weapons programmes.

“It is nonsense to use our legitimate joint training and combined defence posture with the US, which were to respond to North Korea's advanced nuclear and missile threats, as an excuse for launching a reconnaissance satellite,” ministry spokesman Lim Soo-suk told a briefing.

Dave Schmerler, a senior research associate at the James Martin Centre for Nonproliferation Studies, which is part of the Middlebury Institute of International Studies at Monterey, said it was highly unusual for North Korea to be assembling the rocket in daylight, knowing that satellites overhead would be able to watch the site, as opposed to constructing it under a rail-mounted transfer structure, as they have in the past.

“The point is that we’re seeing activity in a launch system that was designed to obscure activity,” Mr Schmerler told the AP. “So this is new and interesting because it’s not using the usual processes.”

Meanwhile, North Korean workers appear to also have quickly built in the span of a month a new launch pad 2.7 kilometres south-east of the launch pad where the activity Tuesday was seen.

That site also appears to have a rail-mounted transfer system, freshly paved asphalt, lightning towers, floodlights and a stand for cameras.

Given that North Korean leader Kim Jong-un is likely to attend the satellite launch, Mr Schmerler said officials at the missile site probably wanted to show off its new facilities. That also would allow for a second launch, if North Korea chose to do so.

“When Kim shows up, he’s not going to be underwhelmed. He should be fairly impressed they just threw this whole thing together,” Mr Schmerler said. “They’re going to use this. Now when they use it, we don’t know.”