"We will each work with Ukraine on specific, bilateral, long-term security commitments and arrangements towards ensuring a sustainable force capable of defending Ukraine now and deterring Russian aggression in the future," the G7 said in a statement obtained by AFP.

Ukraine's international backers are looking to reassure Kyiv on their support after military alliance NATO refused to offer the war-torn country an invitation to become a member.

The group of seven leading democracies -- the United States, Britain, France, Germany, Italy, Canada and Japan -- said they would look to agree on providing Ukraine's forces with "modern military equipment, across land, air, and sea domains".

That would mean "prioritising air defence, artillery and long-range fires, armoured vehicles, and other key capabilities, such as combat air," the statement said.

The global powers said that they would offer to provide swift military and financial assistance to Ukraine "in the event of future Russian armed attack".

They would also look "to impose economic and other costs on Russia" if it launched another war once this conflict is concluded.

Ukraine's President Volodymyr Zelensky had earlier welcomed the promises -- made on the sidelines of a NATO summit in Vilnius -- but said that they could not be a substitute for Kyiv's ultimate goal of joining the alliance.

NATO countries -- spearheaded by the United States -- have been wary of giving Ukraine too concrete a commitment on future membership in the bloc for it fear it will drag the West into war with Moscow.

But Western leaders insist they want to show the Kremlin that it cannot wait for their support to Ukraine to falter.