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, UK and 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 13 people according to the local governor.
Dialling into the luxury hotel spa where the summit is being held, President Volodymyr Zelenskyy 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 said.
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.