Russia is expected to soon start the process to unilaterally annex the Ukrainian regions it controls.

Pro-Russian forces conducted what they call referendums in the eastern regions of Donetsk and Luhansk, Zaporizhzhia in the southeast and Kherson in the south. They said on Tuesday most of the voters were in favor of joining Russia.

On Wednesday, senior officials of pro-Russian forces in Luhansk and Kherson signed documents asking Russian President Vladimir Putin to incorporate their regions into Russia.

Russia's lower house will hold a plenary session on October 3, and the upper house is also expected to deliberate annexation legislation the following day.

The Russian Foreign Ministry said in a statement that a critical stage is approaching in joint efforts to realize the desire of the residents in the four regions to be together with Russia.

Meanwhile, Russian presidential spokesperson Dmitry Peskov hinted that the country will continue its military aggression against Ukraine.

He said the military controls the whole areas of the Luhansk region but acknowledged it has yet to occupy the entire Donetsk region. He said Russia should at least "liberate" the whole of Donetsk.