In December 1999, then--Chinese president Jiang Zemin (江澤民) and then-Russian president Boris Yeltsin signed a protocol in Beijing by which China ceded to Russia territories north of the Amur (Heilongjiang) River and south of the Stanovoy (or Outer Khingan) Range, lands east of the Ussuri River, the Tannu Urianhai region and Sakhalin (Kuye) Island.
Source: wiktionary