The "Donetsk People's Republic" has formally asked Russia to consider its accession to the Russian Federation just hours after voting for independence from Kiev.
Denis Pushilin, the self-proclaimed leader of the separatist republic, has requested that Moscow consider the absorption of Donetsk.
"We, the people of Donetsk, based on results of the May 11 referendum and the declaration of sovereignty of the Donetsk People's Republic, declare that from now on DPR is now a sovereign state," Denis Pushilin said.
Roman Lyagin, another separatist leader and head of the rebel Donetsk election commission, said that joining Russia "would probably be an appropriate step" following the referendum.
Both Kiev and Brussels have declared the separatist vote illegal, while Russia declared that it was important to begin "implementing" the result.
A Kremlin statement said the referendum demonstrated "the will of the people" amid a "high turnout".
Separatists in the regions of Donetsk and Luhansk claim that both received a vote of 89 percent and 96 percent respectively for "self-rule".
It alleged "attempts to disrupt the votes, with the use of force, including the use of heavy weapons, against civilians".
The European Union has imposed further sanctions on Russia - two Crimean companies and 13 individuals - for its actions in the region.