Ukraine is able to launch counterattacks against invading Russian forces even as it defends itself, a military adviser to Ukrainian President Volodymyr Zelenskyy said on Thursday.

"Help to us is increasing every minute and the strength of the enemy is decreasing every minute. We're not only defending but also counterattacking," he said in a televised briefing.

Russia's war on Ukraine, which began Feb. 24, has met with international outrage with the European Union, the United States and the United Kingdom, among others, implementing tough financial sanctions on Moscow.

Many countries are also supplying Ukraine with weapons and have shut airspace to Russian airlines and banned Russian state-run media.

Russia and Ukraine are set for the second round of peace talks Thursday. The first was held Monday.

Earlier Wednesday, Ukrainians said they were battling on in the port of Kherson, the first sizeable city Russia claimed to have seized, while airstrikes and bombardment caused further devastation in other cities, especially Kharkiv in the east.