Leaders of the world's seven richest nations have promised to support Ukraine "for as long as it takes" on the second day of a summit in Germany.
In a statement, the G7 group also said that Russia must stop blocking food from leaving Ukraine's ports.
Addressing the summit via video-link, Ukraine's president appealed for more heavy weapons from Western allies.
G7 leaders are under pressure to be united in their approach against increasing Russian aggression.
"We will continue to provide financial, humanitarian, military and diplomatic support and stand with Ukraine for as long as it takes," they said in a strongly worded statement on Monday.
"We remain appalled by and continue to condemn the brutal, unprovoked, unjustifiable and illegal war of aggression against Ukraine by Russia and aided by Belarus."
The G7 leaders - Canada, France, Germany, Italy, Japan, the UK and the US - have been joined in Bavaria, Germany by two representatives from the European Union.
The high-level talks were held as Russian forces escalated their attacks on Ukraine, where officials said a busy shopping centre was struck by a missile in the central city of Kremenchuk, killing at least ten people according to the local governor.
Dialling into the luxury hotel spa where the summit is being held, President Volodymyr Zelensky asked for more heavy weapons for Ukraine and said he hoped the war would be over by the end of the year "before winter sets in". There are concerns that harsh winter conditions will make battle conditions tougher for Ukraine's troops.
He also urged Western allies to keep the pressure on Russia with more sanctions.
In their joint statement, the G7 leaders said they remain committed to "sustaining and intensifying" sanctions against President Vladimir Putin's government and enablers in neighbouring Belarus. There will be sanctions on gold and oil exports and also "targeted sanctions on those responsible for war crimes", the joint statement said.
The G7 also demanded that the Kremlin allow food to leave Ukraine's ports - and blamed Moscow for rising threats to global food insecurity as a result of the conflict.
Much of Ukraine's highly valued grain exports are in danger of rotting in local warehouses as Russian forces continue blocking Ukraine's ports on the Black Sea.
"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," the G7 statement says.
A BBC investigation has also found evidence that Russian forces in occupied areas of Ukraine have been systematically stealing grain and other produce from local farmers.
Speaking from the summit, UK Prime Minister Boris Johnson told the BBC "the price of freedom is worth paying" in supporting Ukraine, and that help must continue to be offered to rebuild its economy, export grain and protect its citizens.
Earlier on Monday, Mr Johnson was caught on camera making fun of Vladimir Putin - who is a fan of posing shirtless for photos - telling the other world leaders they should "show [Russia] our pecs".
While the G7 leaders were meeting on Monday, reports emerged that Russia had defaulted on its debt for the first time since 1998, after missing a $100m payment deadline. However the Kremlin said the issue is "not our problem", because the payment had been made in May, but had been blocked by Western sanctions.
World leaders have gone out of their way to put on a show of solidarity.
The strongly worded statement they issued today suggests they genuinely are united in their conviction that there is only one way forward, and negates suggestions that some were starting to waver in their support for Ukraine.
The war is, after all, exacerbating a cost of living crisis which is hurting their voters. It also - for now at least - appears to dismiss the controversial claim, put forward by analysts and politicians worldwide, that the war could end if Ukraine hands over territory taken by Russian troops to Vladimir Putin in exchange for peace.
The leaders state that Ukraine, and Ukraine alone, will determine its future, without external pressure.
But the ongoing support will come at a price, which is why the G7 is also focusing on attempts to alleviate the impact on global food and energy supplies.
And it's why they're trying to intensify pressure on Vladimir Putin, discussing new sanctions aimed at cutting off the sources of revenue paying for his war.
But as the German chancellor Olaf Scholz tweeted earlier, tough but necessary decisions lie ahead. Because, given the Russian leader's intransigence to date, their latest demand he withdraw his troops immediately and unconditionally is extremely unlikely to be met.