Russia is planning a second major military base near the border with Ukraine, where NATO accuses Russian troops of helping pro-Moscow separatists fight Kiev's forces.
The new base will house 5,000 soldiers and heavy weaponry, according to public documents and people working at the site.
It is farther east than another base reported under construction in the Belgorod region earlier this month, but still close to the border with separatist-held parts of Ukraine's eastern Luhansk region, where there has been heavy fighting.