Russian forces are continuing to strike targets across Ukraine with missiles, including the capital, Kyiv.

Russia's defense ministry said on Friday that the production facilities of a rocket and aerospace company in Kyiv were destroyed with long-range missiles.

The ministry also said Russian forces used Kalibr cruise missiles to destroy three railway electric power substations in the Kyiv and Odesa regions.

Meanwhile, Britain's defense ministry said Russian territorial gains in eastern Ukraine have been limited due to strong resistance, and have been achieved at significant cost.

A senior US Department of Defense official said on Thursday that Russian forces had made some advances east of the city of Izyum in Kharkiv region to the south, but that the Ukrainians continued to push back.

Ukraine has been on maximum alert for Russian moves to gain undisputed control of southern and eastern Ukraine.

The US ambassador to the Organization for Security and Cooperation in Europe, or OSCE, Michael Carpenter, warned that the Kremlin may be preparing illegitimate referendums in areas of southern and eastern Ukraine, where it claims Russian forces are in full control.

He also warned that Russia may soon stage an illegitimate referendum in the Kherson region of southern Ukraine.

Carpenter added that these referendums would no doubt be accompanied by a wave of abuses against those who oppose Moscow's plans.