Internet connectivity in Ukraine has been affected by the Russian invasion, particularly in the southern and eastern parts of the country where fighting has been heaviest, internet monitors said on Saturday.

Russian forces captured the southeastern Ukrainian city of Melitopol on Saturday, Russia's Interfax news agency reported, as Moscow launched coordinated cruise missile and artillery strikes on several cities, including the capital Kyiv.

Connectivity to GigaTrans, Ukraine's main internet provider, dropped to below 20% of normal levels before returning to higher levels in the early hours of Friday morning, according to internet monitoring organisation NetBlocks.

"We currently observe national connectivity at 87% of ordinary levels, a figure that reflects service disruptions as well as population flight and the shuttering of homes and businesses since the morning of the 24th," Alp Toker, director of NetBlocks, told Reuters.

"While there is no nation-scale blackout, little is being heard from the worst affected regions, and for others there's an ever-present fear that connectivity could worsen at any moment, cutting off friends and family," Toker said.

The Monash IP Observatory in Australia said that so far only the Obolonskyi district of Kyiv and central parts of Kharkiv, in Ukraine's east, showed clear signs of internet failure.

Other anomalies might simply be due to some people moving away from their computers, for example by leaving cities, said Simon Angus, an associate professor of economics who serves as the observatory's director.

Meanwhile, Ukrainian officials released more information about an alleged Belarusian cyberespionage operation they said was targeting personal email accounts belonging to Kyiv's forces.

In a Facebook post, Ukraine's Computer Emergency Response Team said the hackers were targeting not just Ukrainians but also Poles, Russians, and Belarusians as well - including several Belarusian media organisations.

Emails sent to the Belarusian embassy in London were not returned.