KYIV, Ukraine -- Ukrainian President Volodymyr Zelensky said on Tuesday Russia was increasing its attacks across the front line, as Kyiv called for the West to boost its weapons supplies ahead of winter.

Neither side has made any significant territorial gain for months, but both Zelensky and the Kremlin have denied the conflict has ground to a stalemate.

"The military reported an increase in the number of enemy assaults," Zelensky said in a post on social media, saying Russians were attacking around the cities of Donetsk, Kupyansk and Avdiivka.

Zelensky has warned Russia is likely to increase air strikes against Ukraine's energy infrastructure ahead of the winter, as it did this time last year.

Andriy Yermak, Zelensky's chief of staff, met US Secretary of State Antony Blinken in Washington on Monday to press Ukraine's need to keep the flow of Western weapons coming.

"As winter approaches, we expect the Russian missile terror to intensify," Yermak said in a post on Telegram after the meeting.

"Therefore, we are in dire need of air and missile defence systems that will protect Ukrainian cities, key critical infrastructure facilities, and grain corridor routes," he said.

Zelensky on Tuesday called Russian rocket and artillery strikes on the city of Kherson "revenge" and said they were "without any military necessity."

Russian hits on Kherson, which Ukraine retook from Russian forces one year ago, killed three people and wounded at least 12 on Monday, Ukrainian officials said. (AFP)