President Emmanuel Macron of France seems open to increasing the pressure on Iran.

That's my takeaway from Macron's unannounced meeting with Crown Prince Mohammed bin Salman in Riyadh Thursday.

After all, by visiting Riyadh at the end of a visit to the United Arab Emirates, Macron is signaling his clear desire to improve relations between the Sunni-Arab monarchy. Macron offered tough words towards Iran's chief nonstate ally and client, the Lebanese Hezbollah militia. Through his office, Macron "reiterated the importance France attaches to Lebanon’s stability, security, sovereignty and integrity." This "means having a very demanding stance on those who could threaten any leader," Macron said.

With these words, Macron is challenging the Lebanese Hezbollah and, by association, Iran, for their apparent role in forcing Saad Hariri to step down last weekend as Lebanese prime minister.

In turn, the Trump administration might do well to engage with Macron on the Lebanon question. By deposing Hariri, Iran has issued its first major challenge to President Trump's new strategy towards it. And if Trump fails to counter Iran on an exigent issue like that of Lebanon, his strategy will be dead before it even begins.

One solution might be for France to arrange a regional summit in Paris to address the crisis in Lebanon. Putting Iran on notice, the U.S. could then propose new sanctions in the event Iran's malevolent activity continued.

Still, Macron's visit was good for one other reason: It showed that France shares Trump's support for bin Salman. As Macron's office put it, "France supports the development strategy of the Crown Prince defined in his vision 2030 and salutes his speech on the opening of his country and support for a moderate Islam."

This will give bin Salman added international credibility as he pushes forward with his reform agenda, but it will also concern Iran that France seems to have entered his corner.

Ultimately, all of this gives leverage towards one broader objective: unifying joint U.S.-European Union action towards improving the Iran nuclear deal.