North Korea appears to be rebuilding a key long-range rocket test site it promised to scrap, in a possible sign of its displeasure over the collapse of nuclear talks at the second summit between leader Kim Jong Un and U.S. President Donald Trump, experts say.

On Tuesday, the Center for Strategic and International Studies (CSIS) and the 38 North think tanks separately issued reports citing commercial satellite imagery showing that Pyongyang had restored part of the Sohae Satellite Launching Station, which it began to dismantle after pledging to do so at Kim's first summit with Trump last June.

The Sohae facility, which is also known by the name of its location, Tongchang-ri, is the site from which Pyongyang launched satellites in 2012 and 2016. It is also the site of a test stand that the North has used to fire some of its most powerful rocket engines on the ground.