Addressing the G7 summit by videolink, Zelenskyy said battle conditions would make it tougher for his troops as they mount their fightback, and urged the G7 leaders to do the maximum to end the war by year's end, a source told AFP.

The Ukrainian leader asked the assembled heads of state to "do everything" they can, according to German newspaper Welt.

Speaking to the leaders of Britain, Canada, France, Germany, Italy, Japan and the United States on Monday, he asked for a broad range of military, economic and diplomatic support.

Germany's Chancellor Olaf Scholz, acting as G7 president, reaffirmed the group's support for Ukraine.

He tweeted: "We will continue to increase pressure on Putin. This war has to come to an end."