Institute: North Korea resumes work at old launch site

New construction at a North Korea missile launch site is intended to make the location capable of handling larger rockets, a U.S. research institute said Friday.

The work resumed after a months-long hiatus at Tonghae, on the country's northeast coast, on what looks like a rocket assembly building and a launch control center, commercial satellite imagery shows.

The findings were provided to The Associated Press ahead of publication by 38 North, the website of the U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies.

It's the latest sign that North Korea is pressing ahead with its nuclear and missile programs despite declaring its willingness to resume aid-for-disarmament negotiations.

Overhead photos have also indicated the North restarted a mothballed plutonium reactor in late August and is working to upgrade its other main missile launch site at Sohae.

But 38 North says a rocket test doesn't appear imminent at either launch site.

Assessing the intentions of North Korea's secretive regime and the nation's technical capabilities is notoriously difficult. The conclusions are based on imagery analysis by Nick Hansen, a retired intelligence expert who closely monitors developments in the North's weapons programs.

Sohae, which lies on North Korea's west coast, has been used for its recent major launches, including the firing of a three-stage rocket into space last December. That launch was viewed by the U.S. as a worrying marker in the North's development of ballistic missile technology.

In the meantime, Tonghae has been left idle, but experts in 2012 detected construction of a new launch pad to accommodate larger rockets.

That work had appeared to be on hold since early 2013, but images taken between Sept. 16 and Nov. 18 show a roof has been built atop the new launch control center and walls erected for the rocket assembly building. There's no sign, however, of further construction yet at the new launch pad itself and on an access road.

Even though 38 North says completion of all the new facilities at Tonghae may take until 2017, combined with construction activity at Sohae, where a new launch pad for mobile ballistic missiles appears in the works, North Korea seems to be scaling up its capabilities.

In February, the North conducted its third nuclear test explosion, which likely allowed it to make progress in miniaturizing an atomic device it could mount on a missile. It has also paraded mobile, intercontinental ballistic missiles that could potentially reach America, although there's debate about whether the missiles it displayed were just mock-ups.

Earlier this month, Adm. Samuel Locklear, the chief of U.S. forces in the Pacific, said North Korea wants the world to believe that it has such a missile, so he's bound to take that threat seriously.

Pyongyang has enshrined its drive to build a nuclear arsenal in its constitution but also says it is willing to restart international nuclear talks it withdrew from five years ago.

The U.S. says it will only negotiate with North Korea if it first takes concrete actions to demonstrate its sincerity about the goal of disarmament.

The Associated Press contributed to this report.