Foreign ministers from the Group of Seven developed nations, including US Secretary of State Antony Blinken, are gathering on the Italian island of Capri from Wednesday to Friday.

Ukrainian Foreign Minister Dmytro Kuleba joined counterparts from Italy, the UK, the US, Japan, Canada, France and Germany for a working session dedicated to the conflict on Thursday.

Kuleba called for other countries to follow Germany, which at the weekend said it was sending an additional Patriot air defence system to Kyiv.

"We will work here at the ministerial (meeting) to make other allies deliver air-defence systems to Ukraine, because it's of fundamental importance," Kuleba told reporters ahead of the session.

Ukraine has said it is running out of weaponry to shoot down Russian missiles and drones as Moscow has ramped up its attacks on infrastructure across the country.

Stoltenberg said there had been "important, encouraging signs" of new support from NATO allies, including the scheduling of a US Congressional vote this weekend on a long-stalled $61-billion-euro package of aid.

"It's of vital importance that NATO allies sustain and step up their support... There's an urgent, critical need for more air defence," Stoltenberg said.

Earlier, Blinken stressed the need for the US Congress to agree the new aid.

"At this moment, it is urgent that all of the friends and supporters of Ukraine maximise their efforts to provide... Ukraine with what it needs to continue to effectively defend itself against the Russian aggression," Blinken said.

Kubela said the help would "literally, without exaggeration, help save Ukrainians from Russian missile slaughter".

"This is a matter of death and life."

After the day's talks, Italian Foreign Minister Antonio Tajani -- whose country holds the rotating G7 presidency this year -- said allies had confirmed "our maximum commitment" to Kyiv.

He confirmed ministers discussed the potential use of Russian assets frozen after the February 2022 invasion to help Ukraine.

"We are evaluating (the idea) in principle, we are also in favour of using the seized assets, but we need the legal basis to do so," Tajani said.

British Foreign Minister David Cameron called earlier in Capri for "creative" way of using the assets, saying it was "important we try and get agreement" on how.

There have been mounting calls in Washington and Europe to set up a fund for Ukraine using billions of dollars in Russian bank accounts, investments and other assets frozen by the West after the invasion.

The EU froze some 200 billion euros of Russian central bank assets held in the bloc as part of sanctions on Moscow.