Joe Biden told the G7 that Putin “will not break our resolve" in supporting Ukraine on Sunday on the summit’s final day.
Speaking at a press conference in Japan, the US president said he has recieved a “flat assurance” from Kyiv that Western-provided F-16 fighter jets would not go into Russian territory.
These powerful warplanes, which are being sought by Ukraine, could be used “wherever Russian troops are within Ukraine and the area", he said.
But Mr Biden said it was “highly unlikely” the planes would be used in any Ukrainian offensive in the coming weeks, but that troops could need such weapons to defend themselves.
Earlier, Mr Biden announced a $375 million (£301m) package of military aid, including artillery and armoured vehicles, for Ukraine.
Ukraine’s Volodymyr Zelensky has used an appearance at the summit to push western allies to send the warplanes, prompting Russia to warn of “colossal risks” and accuse the West of escalation.
Despite the threat, the US President said the G7 had “reaffirmed our shared and unwavering, let me say it again, our shared and unwavering commitment to stand with the brave people of Ukraine as they defend themselves against Russia's brutal war of aggression and the war crimes being committed”.
He added: “Together with the entire G7, we have Ukraine’s back and I promise we’re not going anywhere.”
Western allies also vowed on Sunday that they would not back down from supporting Ukraine, in a warning to Vladimir Putin as he claimed to have taken the eastern city of Bakhmut. This is denied by Kyiv, which insists the city is not occupied by Russia.
He told reporters that he had discussed the issue of sending F-16 jets to Ukraine during a private meeting with Volodymyr Zelensky.
He said F-16s would not have helped Ukrainian forces with regard to Bakhmut but could “make a big difference in terms of being able to deal with what is coming down the road".
Mr Biden said separately that the G7 had agreed a united approach to China which called for countries to reduce their reliance on China.
“We’re not looking to decouple from China. We’re looking to de-risk and diversify our relationship with China,” he said.
He said the countries were united in “resisting economic coercion together and countering harmful practices that hurt our workers."
G7 leaders outlined a shared approach to "de-risk, not decouple" economic engagement with China in a statement on Saturday, prompting China to complain to Japan which is the summit organiser.
Despite the reaction, Biden said he expected a thaw in frosty relations with China “very shortly" after strains caused by an incident earlier this year when the United States shot down a Chinese balloon that flew over sensitive military sites.
On tensions between China and Taiwan, Mr Biden said there was a clear understanding among most of the allies that if China were to act unilaterally against the self-governed island Taiwan, there would be a response.
“We’re not going to tell China what they can do," he said. “But in the meantime we’re going to put Taiwan in a position where they can defend themselves.”
