The killings of 129 people in multiple attacks on Paris on Friday have resulted in calls for a NATO campaign against the Islamic State, which claimed responsibility for the carnage.

“That’s a decision for the French to make,” Ben Rhodes, the White House’s deputy national-security adviser, said on NBC’s Meet the Press. “What we’ve made clear to the French is we will be shoulder to shoulder with them in this response.”

At issue is Article 5 of NATO’s charter, which states that an attack on one member of the alliance is an attack on all of them. A response is based on the principle of collective defense. The article has been invoked just once in NATO’s more than six-decade history: after the attack of September 11, 2001.

In an interview with NPR, Admiral James Stavridis, a former NATO-allied supreme commander, pointed out the attacks in Paris were similar to the attacks of September 11.

“I do [think that], and I think the French very much do. Any nation of the 28 in NATO has the authority to request an Article 4 consultation, which leads to an Article 5 declaration. I think France will do that. And I think they have pretty good - pretty good, valid grounds for that, particularly if you put the death level and the injury level on a population-adjusted basis - population of France about one-sixth that of the United States - this really starts to resemble a 9/11 level event. …

I think a NATO response would be four or five things. It would start with an enhanced level of intelligence-sharing and special operations from the NATO nations going in and supporting the current campaign. Secondly, NATO would take over the bombing campaign. This would bring many more assets - aircraft ordinance, the airborne early warning aircraft - into the fight. Thirdly, I think NATO should take on the training mission, both for the Kurds in the north and the Iraqi security forces in the south. [T]his way the United States doesn't have to pull the entire load. We need the alliance to step up and be there with us. And by the way, this ought to be not just NATO. There are many Arab states - and indeed Russia at least has articulated a desire to conduct operations as part of this - so I see this as NATO as the core of, effectively, a global response against the Islamic State.

Separately, Stavridis predicted to the BBC NATO will put “boots on the ground” against the Islamic State. He said he expected 10,000 to 15,000 of the alliance’s troops would be required.

Defense Secretary Ash Carter spoke with his French counterpart, Jean-Yves Le Drian, the Defense Department said in a statement, and discussed the campaign against the Islamic State.

“They agreed on concrete steps the U.S. and French militaries should take to further intensify our close cooperation in prosecuting a sustained campaign against ISIL,” Peter Cook, the Pentagon’s spokesman, said.  

He did not elaborate on what those steps may be, but The Wall Street Journal reported the U.S. would expand intelligence sharing with France “and has agreed to speed the delivery of detailed targeting information in support of possible French retaliatory strikes against Islamic State militants in Syria and Iraq.”

Here’s more:

France has fighter aircraft positioned at bases in the region, in Jordan and the United Arab Emirates, which could be used in any retaliatory strikes against Islamic State in Syria and Iraq once targets have been identified.

French officials said France could step up its strikes in Syria and Iraq against Islamic State targets within days, including strikes based on the intelligence provided by the U.S.

Indeed, Le Figaro reported France began conducting airstrikes against Raqqa, the Syrian city that serves as self-declared capital of the Islamic State.

Kristian Jense, the foreign minister of Denmark, a NATO member, said the country’s fighter jets, which were in action in Iraq earlier this year, should have the mandate to bomb Islamic State positions in Syria when they return to the Middle East next year, Reuters reported. Such a move would need parliamentary approval.

In Antalya, Turkey, Sergei Ryabkov, the Russian deputy foreign minister, said he hoped the attacks would help Russia and the West bridge their differences.

“We hope that the events in Paris maybe after all will clear the air and will change the scale of priorities of our colleagues in Washington and in other NATO capitals a little bit,” he said on the sidelines of a meeting of the Group of 20 nations.

Russia and the West are both fighting against the Islamic State in the Syrian civil war—but on opposite sides of the conflict. Russia is conducting military operations in support of President Bashar al-Assad against the Islamic State and other rebel groups, including some that are backed by the West. The U.S. and its allies say they want Assad to step down and are targeting the Islamic State with airstrikes while providing limited support to some other rebel groups that are fighting the Syrian leader.

In Antalya, President Obama met Sunday with his Russian counterpart, Vladimir Putin, on the sidelines of the G20 summit for 35 minutes. Yuri Ushakov, the Kremlin’s top foreign-policy adviser, said while the two leaders shared the “strategic goals regarding the fight against Islamic State … they still differ as far as tactics are concerned.”