The US has proposed Ukraine be protected by a NATO-style collective defense guarantee to allay fears of renewed Russian aggression in the event of a peace deal, Italy's premier and diplomatic sources said Saturday.

The suggestion was raised during a call US President Donald Trump held with Ukrainian President Volodymyr Zelensky and European leaders Saturday, the day after Trump's summit with Russia's Vladimir Putin.

"As one of the security guarantees for Ukraine, the American side proposed a non-NATO Article 5 type guarantee, supposedly agreed with Putin," one diplomatic source told AFP on condition they not be identified.

Article 5 is a cornerstone of the NATO Western military alliance, stating that if one member is attacked, the entire alliance comes to its defense.

Kyiv has long aspired to join NATO, but Russia has given that as one of its reasons for its war in Ukraine — and Trump has repeatedly ruled out the idea.

Instead, Italian Prime Minister Giorgia Meloni has been pushing a proposal that would bring Ukraine under NATO's defense umbrella even without being a member — an idea she said Trump raised in Saturday's call.

Another source with knowledge of the matter confirmed that NATO-like guarantees had been discussed.

But that source added: "No-one knows how this could work and why Putin would agree to it if he is categorically against NATO and obviously against really effective guarantees of Ukraine's sovereignty."

Meloni's statement made no mention of whether the idea had been discussed with Putin.

Defensive security

US Secretary of State Marco Rubio said Thursday that security guarantees for Ukraine needed to be part of peace talks.

Britain and France have said they are prepared to deploy troops to Ukraine to help preserve any truce.

But Meloni — who has ruled out sending Italian troops -- has presented her proposal as a less risky, less expensive compromise.

On Saturday, she said the starting point would be to define a collective security clause "that would allow Ukraine to benefit from the support of all its partners, including the US, (which would be) ready to act in case it is attacked again".

In March, Meloni told Italian senators that Article 5 was not necessarily about going to war, saying force was only one possible option when called upon to help an ally.

She also said the collective defense agreement went both ways, suggested other NATO countries could benefit from the protection of the Ukrainian army if needed.

Crucially, she said, the plan would require Russia to put its cards on the table.

"If Moscow has no intention of invading (Ukraine) again in the future, what would be the reason for opposing merely defensive security guarantees?" she said in March.

Keir Giles, from Britain's Chatham House think tank, told AFP on Saturday that the idea was "intriguing".

"If taken literally, (it) could provide the kind of essential ingredient to a lasting peace settlement that European powers have been requesting," he said.

But he warned the lack of detail mean "we cannot tell at the moment whether this is in fact a meaningful contribution toward a peace settlement, or another use of potentially deceptive wording which might offer the semblance of a security guarantee while in fact providing no protection against Russia at all".