The divergence highlights divisions in the West over how to deal with the Iranian-backed Houthis, who have been targeting civilian ships in the Red Sea for weeks in what they say is a protest against Israel's military campaign in the Gaza Strip.
US and British warplanes, ships and submarines launched dozens of air strikes across Yemen overnight in retaliation for the repeated Houthi attacks on one of the busiest commercial shipping routes in the world.
The Netherlands, Australia, Canada and Bahrain provided logistical and intelligence support for the operation, US officials said.
In addition, Germany, Denmark, New Zealand and South Korea signed a joint statement with these six nations defending the overnight attacks and warning of further action to protect the free flow of Red Sea trade if the Houthis did not back down.
A source in Prime Minister Giorgia Meloni's office said Italy had declined to sign the statement and as a result was not asked to participate in the attacks.
However, a government source said Italy had been asked to take part but declined for two reasons -- firstly because any Italian involvement would have needed parliamentary approval, which would have taken time, and secondly because Rome preferred to pursue a "calming" policy in the Red Sea.
Hours later, a government statement added that "Italy supports the operations of allied countries, who have the right to defend their vessels, in the interest of global trade flows and humanitarian assistance."
Speaking on condition of anonymity, a French official said Paris feared that by joining the US-led strikes, it would have lost any leverage it had in talks to defuse tensions between Hezbollah and Israel. France has focused much of its diplomacy in recent weeks on avoiding an escalation in Lebanon.
Asked whether France refused to participate, US National Security Council spokesman John Kirby said he wouldn't elaborate on diplomatic conversations.
"You've seen the list of people that participated," he said. "Internationally, even those who weren't actively involved in the dropping of bombs - many of our coalition partners had signed up to the support, non-operational support."
Signalling possible tacit support for the US action, the French foreign affairs ministry issued a statement saying the Houthis bore responsibility for the escalation.
However, a diplomat who is aware of France’s position said Paris did not believe the attack could be deemed legitimate self-defence.
The United States is "very comfortable and confident in the legal authorities that the president exercised to conduct these strikes," Kirby said.
Spanish Defence Minister Margarita Robles said Madrid had not joined the military action in the Red Sea because it wanted to promote peace in the region.
"Every country has to give explanations for its actions. Spain will always be committed to peace and dialogue," she told reporters in Madrid.
Italian Defence Minister Guido Crosetto earlier this week, made clear his reluctance to target the Houthis, telling Reuters that their aggression had to be stopped without triggering a new war in the region.
The diverging opinions in the West over how to tackle the Houthi threat emerged last month when the United States and a number of its allies launched Operation Prosperity Guardian to protect civilian vessels in the busy Red Sea shipping lanes.
Italy, Spain and France did not sign up to the mission, unwilling to put their naval vessels under US command.
All three already participate in an EU anti-piracy operation off the Horn of Africa, and the Spanish defence minister on Friday said the European Union might soon decide on a new initiative.
"The EU could decide ... in a few days' time that there should be a (naval) mission. We do not yet know the scope if that mission is approved, but in the meantime Spain's position out of a sense of responsibility and commitment to peace is not to intervene in the Red Sea," she said.
