Syria has allowed Russia to significantly expand its naval facility in the Mediterranean port of Tartus and keep using it for decades to come.
The facility is the only such outpost Russia has outside the former Soviet Union. The Russian military has used Tartus to back its campaign in support of Syrian President Bashar Assad.
Under the agreement released on Friday, Syria has offered Russia free use of the Soviet-era facility for 49 years. The term can be automatically extended for further 25-year periods if neither side objects.
The deal signed in Damascus also allows Russia to modernize the site so that it can host up to 11 ships at a time, including the nuclear-powered ones. Now Tartus only has room for a couple of mid-sized ships at a time.