KYIV, Ukraine (AFP) — Ukraine said Sunday its forces were working to wrest control of towns and villages around the strategic hub of Izyum from Russian troops as part of a sweeping counter-offensive in the country's east.

"Our forces entered Kupiansk. The liberation of settlements in the Kupiansk and Izyum districts of the Kharkiv region is ongoing," the Ukrainian military said in a general battlefield update Sunday, 200 days into Russia's invasion.

A Ukrainian push to dislodge Russian forces has seen at least 30 towns and villages in the eastern Kharkiv region retaken by Kyiv's army.

The military said in its update Sunday that Ukraine captured over 3,000 square kilometers from Moscow's forces in recent days.

Russia first said it was reinforcing the Kharkiv region but on Saturday announced it was pulling back troops to the Donetsk region further south.

Meanwhile, Ukraine said Sunday the sixth and final reactor at the Russian-controlled Zaporizhzhia nuclear power station in the south of the country was no longer generating electricity.

"Today, September 11, 2022, at night, at 03:41 a.m., unit No. 6 of the ZNPP was disconnected from the power grid. Preparations are underway for its cooling and transfer to a cold state," state nuclear agency Energoatom said in statement.

Ukraine and its allies have been increasingly concerned about the safe operation of the Zaporizhzhia plant — the largest in Europe — and recent fighting there has raised fears of serious incident.

The United Nations' atomic watchdog warned earlier this week that a blackout in the nearby town of Energodar had "compromised the safe operation" of the nuclear facility.

Energoatom said Sunday that a cold shutdown was the "safest state" for the reactor.

Energoatom said that the sixth reactor had been generating energy for the plant itself for three days and that the decision to halt its operations came when external power had been restored to the facility.

"In case of repeated damage to the transmission lines linking the facility to the power system — the risk of which remains high — the (plant's) in-house needs will be powered by diesel generators," it cautioned in a statement.

Energoatom in its statement again called for the establishment of a demilitarized zone around the plant, saying it was the only way to ensure the plant's safety.