Ukraine urgently needs to boost its air defences in the face of relentless Russian attacks, Germany's top diplomat said on Tuesday as she arrived in Kyiv.

The visit from Foreign Minister Annalena Baerbock came as more than two dozen Russian drones targeted Ukraine overnight, in an attack that left several wounded in the eastern Kharkiv region.

"The situation in Ukraine has once more dramatically deteriorated with the massive Russian aerial attacks on civilian infrastructure, and the brutal Russian offensive in the Kharkiv region," Baerbock said as she arrived for her eighth visit to the country since Russia invaded in February 2022.

To protect itself from the "rain of Russian drones and missiles," Ukraine "urgently needs a boosted air defence," she said.

"Our support is based on the deep conviction that Ukraine will win this war," Baerbock said.

Ukrainian President Volodymyr Zelensky warned last week that the Russian ground offensive launched this month in the eastern Kharkiv region may only be a "first wave" and that Russian troops could be aiming for the city of Kharkiv -- the second largest in Ukraine.

He has repeatedly called on Ukraine's allies to provide at least seven more air defence systems, including at least two to protect the Kharkiv region.

Russian President Vladimir Putin believes that Ukraine and its allies will at some point run out of steam, Baerbock said, but "we have the capacity to hold out."

Just before Baerbock arrived, the Ukrainian air force said it had intercepted 28 out of 29 Iranian-designed attack drones launched by Russian forces overnight. The unmanned aerial vehicles were downed over southern and eastern regions of Ukraine.

The head of the Kharkiv region said a 53-year-old man was wounded by Russian rocket fire targeting a transport infrastructure facility.

Systematic Russian attacks on Ukraine's energy grid have crippled the country's energy sector and officials in the capital announced rolling power cuts throughout the day Tuesday to reduce the load on the grid.