A Russian official said Thursday that the ruble will soon be introduced in areas of Ukraine under Moscow's control, despite Russia earlier insisting it was not seeking to occupy captured territory.

A civilian and military administrator of the Russian-controlled region of Kherson in southern Ukraine said Moscow would introduce its currency in the region within the coming days.

"Beginning May 1, we will move to the ruble zone," the official, Kirill Stremousov, was cited as saying by Russia's state-run news agency RIA Novosti.

He specified there will be a grace period of four months when Ukraine's currency, the hryvnia, would also be used.

"Then we will completely switch to settlements in rubles," RIA Novosti quoted Stremousov as saying.

Stremousov's announcement was yet to be confirmed by any high-ranking Russian official.

Ukraine's human rights ombudswoman, Lyudmyla Denisova, condemned the plans as an "act of annexation" and accused Russian forces of "starving the people of Kherson by blocking humanitarian aid" to the city.

"The introduction of the Russian ruble in the region of Kherson is an act of annexation and another gross violation by Russia" of international law, she said.

Russia said earlier this week that it had seized control of the entire southern Kherson region, including its eponymous administrative capital, which fell to Russian troops soon after the February 24 invasion.

Moscow's defence ministry claimed that "peaceful life" was being restored to the region and others which have been captured recently, despite reports in the Ukrainian press and on social media of ongoing protests against the Russian administration of Kherson.