KYIV: Russian forces have taken the Ukrainian city of Kherson, local officials confirmed, the first major urban centre to fall since Moscow invaded one week ago.

"The (Russian) occupiers are in all parts of the city and are very dangerous," Gennady Lakhuta, head of the regional administration, wrote on messaging service Telegram late Wednesday.

The strategic port city of 290,000 people near the Black Sea came under siege as Russian forces pressed ahead with their offensive across other urban centres.

Another key Ukrainian port, Berdiansk, has already been seized by Russian troops, while Mariupol has repelled attacks "with dignity," according to that city´s mayor, Vadim Boichenko.

Russian forces have also bombarded Ukraine's second-biggest city Kharkiv, prompting comparisons to the massacres of civilians in Sarajevo in the 1990s.