"NATO must remain united. I believe it is a source of strength," Meloni told reporters as she attended an EU summit in Nicosia, Cyprus.

The Reuters news agency cited an anonymous US official saying the Pentagon had outlined potential measures to punish allies over their response to the Iran war, including suspending Spain from the alliance.

There is no provision in the NATO treaty allowing for the suspension or expulsion of one of the alliance's members.

US President Donald Trump has repeatedly railed against NATO allies for refusing to help out more with the Iran war, saying he viewed it as a betrayal.

Some of them -- France, Spain and Italy -- did not allow US military aircraft deployed for the war to overfly their territories or to use bases.

Britain initially also refused, but later allowed US flights from its bases for "defensive" missions in the conflict.

Trump also tried, in vain, to get European NATO members to send warships to the Strait of Hormuz, which Iran has effectively closed with military threats and attacks.

Spanish Prime Minister Pedro Sanchez, whose country was reportedly singled out for suspension, said Friday he was "not worried", stressing his country was a "reliable member" of NATO.

Meanwhile, as Trump deepens questions over whether Washington would help defend NATO allies, the EU is set to lay out a "blueprint" for how its own mutual assistance clause works if a country is attacked.

Meloni insisted that NATO would remain central to Europe's defence, but that European nations needed to play a bigger role in their own security.

"We must work to strengthen NATO's European pillar which must clearly complement the American one," she added.