German Foreign Minister Johann Wadephul has arrived in Ukraine on a solidarity visit just days before the country marks the 35th anniversary of its independence, as Russia steps up its military assault on the country.

Wadephul arrived by special train at Kiev's main railway station and condemned Russia's escalating drone and missile strikes, accusing Moscow of the "indiscriminate murder of civilians" and the deliberate destruction of energy infrastructure.

The visit comes days after 16 people were killed in Russian missile strikes on the Ukrainian capital, and one day after a separate attack on a shopping centre in President Volodymyr Zelensky's home city of Kryvyi Rih left at least 15 dead and 130 hurt.

Wadephul said Russia was trying to destroy the livelihoods of the Ukrainian population and break their will to resist.

The summer months of July and August have been the deadliest for the Ukrainian civilian population in more than four years, he said. "Never before has Russia fired more missiles at its neighbouring country."

The German foreign minister pledged further support for Ukraine, expressing hope that Russia could be brought to the negotiating table. He noted that no country invests as much in military and financial support for Ukraine as Germany.

The visit was Wadephul's fourth to Ukraine since taking office 16 months ago. It was not announced publicly in advance for security reasons, as is customary.

His programme in Kiev has also not been disclosed, though talks with the Ukrainian leadership are expected to be the focus.

Ukraine declared independence from the Soviet Union 35 years ago on Monday. Celebrations are taking place around the anniversary, primarily in the capital Kiev.

However, a shortage of air defence units such as Patriot missiles has left the country defenceless against Russian missile strikes, leading Zelensky to plead for more support from Ukraine's Western partners..