The Group of Seven most industrialised countries vowed enduring support for Ukraine in the face of Russian aggression, in a statement from its summit in southern Germany on Monday.

"We will continue to provide financial, humanitarian, military and diplomatic support and stand with Ukraine for as long as it takes," the G7 said.

After speaking with Ukrainian President Volodymyr Zelensky for nearly two hours by video-link from Kyiv, G7 leaders issued a forceful message of solidarity with the embattled nation.

"As G7 we stand united on Ukraine's side and will continue our support. For this, we all have to take tough but necessary decisions," the summit's host, German Chancellor Olaf Scholz tweeted, thanking Zelensky for taking part.

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

Addressing Russia, the G7 said Moscow must allow grain shipments to leave Ukraine to avoid exacerbating a global food crisis.

"We urgently call on Russia to cease, without condition, its attacks on agricultural and transport infrastructure and enable free passage of agricultural shipping from Ukrainian ports in the Black Sea," it said.

Not the time

The leaders also called for Moscow to allow Ukrainians taken to Russia against their will to return home at once. 

"We demand that Russia immediately allow the safe return of Ukrainian nationals taken often with force to Russia without their consent," they said.

The club of rich nations expressed "serious concern" over Russia's stated plans to deliver missiles capable of carrying nuclear warheads to Belarus in the coming months.

"We urge Russia to behave responsibly and exercise restraint," the leaders said.

A G7 source said Zelensky had urged world leaders to do their utmost to end Russia's invasion of his country by the end of the year, as battle conditions would make it tougher for his troops as they mount a viable defence. 

Zelensky stressed the need to keep heaping "heavy" punitive action on Russia, and "not lower the pressure" despite the multiple rounds of sanctions Western allies have unleashed on Moscow.

He said he was not ready to open negotiations with Russia, as Kyiv is still seeking to consolidate its positions, the French presidency quoted him as saying.

"President Zelensky gave a very clear response that now is not the time for negotiations. Ukraine will negotiate when it is in a position to do so, that is, when it has basically re-established a position of strength," Emmanuel Macron's office said.

The Ukrainian leader later said on his Telegram account he had asked leaders to cap the price of Russian oil as a means of depleting the Russian war chest funded in large part by energy revenues.