Severodonetsk -- the largest city still in Ukrainian hands in the Lugansk region of eastern Ukraine -- has been the focal point of fighting in recent weeks.

"The residential areas of the city of Severodonetsk have been fully liberated," Shoigu told a defence ministry meeting in televised remarks.

The Russian army was still seeking to establish control over the city's "industrial zone and the nearest settlements", he added.

Since President Vladimir Putin sent troops into Ukraine on February 24, the Russian army has made significant gains in the east of the country, expanding on territories previously controlled by pro-Moscow separatists.

Russian forces are now in control of the eastern Ukrainian port city of Mariupol, the second busiest in the country before the conflict.

"The de-mining of the Mariupol port is complete. It is operating as normal and has accepted the first cargo ships," Shoigu said.

Shoigu added that 6,489 Ukrainian soldiers have surrendered to Russian troops since the start of Moscow's offensive.