Ukrainian President Zelenzkyy said by video link to the G-7 summit that battle conditions would make it tougher for his troops as they mount their fight to repel Russia's invasion.
He therefore urged the G7 leaders to do their maximum to end the war by year's end, including by intensifying sanctions against Russia, the source said.
Despite the multiple rounds of punitive measures that Western allies have unleashed on Moscow, Zelensky pleaded with them to "not lower the pressure and to keep sanctioning Russia massively and heavily."
His plea to the world's biggest economic powers came along with a call for Western leaders to step up weapons supplies to his country as Russian forces fought to capture Lysychansk, the last big city still held by Ukrainian troops in eastern Luhansk province.
Luhansk governor Serhiy Gaidai said Lysychansk was suffering "catastrophic" damage from shelling as Russian forces targeted the city following the fall of neighboring Sievierodonetsk over the weekend.
"The situation in the city is very difficult," Gaidai wrote on the Telegram messaging app.
In his communication with the G-7, Zelenskyy urged the group to do their maximum to end the war by year's end, including by intensifying sanctions against Russia, the source said.
Despite the multiple rounds of punitive measures that Western allies have unleashed on Moscow, Zelensky pleaded with them to "not lower the pressure and to keep sanctioning Russia massively and heavily."
"Partners need to move faster if they are really partners, not observers. Delays with the weapons transfers to our state, any restrictions - this is actually an invitation for Russia to hit again and again," he said.
On Monday, the Group of Seven rich nations vowed enduring support for Ukraine in the face of Russian aggression, in a statement from its summit in Germany.
"We will continue to provide financial, humanitarian, military and diplomatic support and stand with Ukraine for as long as it takes," the G7 said.
This report was sourced from information provided by Reuters and Agence France-Presse