Ukraine's sovereignty has been threatened since Russian forces occupied Ukraine's Crimea in 2014 and Moscow illegally annexed the peninsula, followed eight years later by the all-out invasion of February 2022.
Statehood Day, celebrating the country's self-determination, is a public holiday in Ukraine.
The war has killed thousands of soldiers and civilians, forced millions to flee their homes, reduced Ukrainian cities to rubble and fuelled fears the confrontation could slide into an open conflict between Russia and NATO, whose member nations have supported Kyiv.
No peace settlement is in sight.
Senior officials from southeastern European countries also visited Kyiv on Wednesday for a periodic gathering focused on Black Sea and regional security.
The 2025 meeting in the southern Ukraine city of Odesa reaffirmed the countries' support for Ukraine's sovereignty and territorial integrity.
Ukrainian President Volodymyr Zelenskiy has recently won important pledges of further support, including from the Group of Seven leading industrialised nations and the so-called Coalition of the Willing countries.
Von der Leyen, the European Union's top official, said her trip to the Ukrainian capital was her 11th in wartime.
Europe is watchful of Russia's broader intentions on the continent and has provided billions of euros to Ukraine as well as diplomatic support.
Von der Leyen said she would announce new steps towards integrating the European and Ukrainian defence industries as well as providing new help to prepare Ukrainian air defences for winter, when Russia usually tries to knock out the power.
Her visit came as Western officials and analysts say Ukraine's increasingly frequent and accurate drone and missile attacks are hitting high-profile targets deep inside Russia, severely disrupting the Russian army's supply lines and causing civilian fuel shortages.
"It's a special moment," Von der Leyen said of her visit on social media.
"Ukraine has built a strong military momentum. The tide is turning."
Meanwhile, Serbia's Moscow-friendly president, Aleksandar Vucic, was taking part in the Southeast Europe Summit in Kyiv.
Serbia, which relies almost fully on Russia for its energy supplies, has refused to join Western sanctions on Moscow that were imposed after its invasion, although it officially supports Ukraine's territorial integrity.
Ukrainian officials said on Wednesday that at least eight civilians were killed and 11 others were injured in Russian aerial attacks.
Russian forces dropped six powerful glide bombs mostly targeting infrastructure in Ukraine's northern Sumy region, killing three people and wounding seven, the head of the regional military administration Oleh Hryhorov said.
Three people were killed and three others wounded in a Russian attack on Odesa, according to the head of the city's military administration, Serhii Lysak.
Also, in Ukraine's northern Chernihiv region, Russian drone attacks killed two people and seriously wounded an 18-year-old, regional military administration head, Viacheslav Chaus said.
In Moscow, the Russian defence ministry said its air defences overnight intercepted 93 Ukrainian drones over several Russian regions, as well as over Crimea and the Sea of Azov and the Black Sea.
