The head of pro-Russian separatists who effectively control part of Ukraine's Luhansk region has expressed his belief that a referendum will be held in the area in the near future to decide whether to join Russia.

Leonid Pasechnik spoke to reporters on Sunday.

A Russian news agency reported that a referendum is supported by lawmaker Andrei Klishas, who heads the constitutional legislation committee in Russia's upper house.

Klishas reportedly said Russia has recognized the sovereignty of the Luhansk and Donetsk People's Republics and the authorities of these republics have the right to make decisions in accordance with their constitutions.

The Ukrainian foreign ministry's spokesperson, Oleg Nikolenko, tweeted, "Fake referendums in the occupied parts of Ukraine are null and void. No country in the world will ever recognize the forceful change of Ukraine's internationally recognized borders." He also wrote that Russia will be further isolated.

A Russian lower house lawmaker, Leonid Kalashnikov, said this is not the right time for a referendum. He said it is hardly necessary to occupy oneself with such questions when the fate at the front is being decided.

Russia's defense ministry said on Friday that Russian backed-separatists had put 93 percent of Luhansk under their control.

In 2014, a referendum was held in Crimea, southern Ukraine, after Russia sent special forces to the region. Russia used the results to defend its annexation of Crimea.

Ukraine, other European countries and the United States did not recognize the voting, saying it was unconstitutional.