British Prime Minister Rishi Sunak will announce up to £242 million in fresh assistance for Ukraine at the G7 summit in Italy set to open on Thursday, his office said.

Ukraine is expected to be top of the agenda at the gathering in Puglia, where President Volodymyr Zelensky will join G7 leaders seeking to seal a deal on using frozen Russian assets to help his war-torn country.

At the summit, Sunak "will announce up to £242 million ($310 million) in bilateral assistance to Ukraine, to support immediate humanitarian, energy and stabilisation needs, and lay the foundations for longer term" recovery, the prime minister's office said in a statement Wednesday night.

"This funding demonstrates the UK's continued international solidarity with Ukraine, and our flexibility in responding to immediate needs created by Russian aggression," it added, noting recent Russian strikes on energy infrastructure.

The statement added that Sunak would work with other leaders at the G7 to find a way to use frozen Russian funds to assist Ukraine.

"We must be decisive and creative in our efforts to support Ukraine and end Putin's illegal war at this critical moment," Sunak was quoted as saying.