Ukrainian forces continue their counteroffensive against Russian troops, and claim that they have recaptured territory in the southern region of the country.

Deputy Defense Minister Hanna Maliar said in a social media post on Monday that the scale of shelling by Russian forces in eastern regions doubled last week, and fierce fighting continues in the key city of Bakhmut.

Maliar also said forces are advancing on Melitopol, one of the main cities of the southern region of Zaporizhzhia, and toward the port city of Berdyansk facing the Azov Sea.

She added that the Ukrainian side had regained about 28 square kilometers of land over the past week.

Washington-based think tank the Institute for the Study of War said on Sunday that "Ukrainian forces reportedly conducted counteroffensive operations in six sectors of the front and made gains in some of these areas."

Meanwhile, the Kremlin said on Monday that Russian President Vladimir Putin sent a congratulatory message to Belarusian President Alexander Lukashenko to mark Belarus's independence day.

The message describes bonds of friendship between the countries tempered in times of war and forming the basis of a relationship that continues to provide mutual support amid threats and challenges from external sources.

Putin has indicated that a storage facility for tactical nuclear weapons in Belarus is scheduled to be completed by early July.

Putin is believed to be sending a warning to the West by deploying nuclear weapons in the country, which is close to Eastern Europe and the Baltic states.