PARIS (Reuters) - When Emmanuel Macron called Vladimir Putin on Friday, the day before launching his first major military operation with strikes on Syria, the French president knew the credibility of his foreign policy was at stake.

FILE PHOTO: French President Emmanuel Macron arrives at an elementary school to attend a one-hour interview with French news channel TF1, in Berd'huis, France, April 12, 2018. REUTERS/Gonzalo Fuentes

Less than a year ago, in the ornate Gallery of Battles of the palace of Versailles, he warned the Russian leader in their first meeting that the use of chemical weapons in Syria would be a red line that would result in reprisals.

“I believe this chemical attack took place, I believe my red line was crossed,” he told Putin in the Friday morning phone call, according to a close advisor at the Elysee palace.

“The tone was very direct, the two presidents were under no illusion about what was going to happen,” the advisor told Reuters on Saturday, soon after the overnight air strikes.

The decision to strike Syrian government targets followed a week of hectic diplomacy and coordination with U.S. and British allies.

Last Sunday evening, Macron sat with a small group of advisors at the Elysee palace to watch numerous graphic images and videos of suffering children following an attack the previous day on Douma, which France and allies say was a chemical attack.

“The president immediately realized the seriousness of these attacks,” the first advisor said.

RED LINE “MEANT TO BE RESPECTED”

After a first phone call with U.S. President Donald Trump that night, a series of painstaking daily meetings with defense and foreign affairs officials took place to check the authenticity of images and information coming from Syria.

On Thursday, sitting in a primary school in Normandy where he was giving his first TV interview in months, Macron said France now had proof the Syrian government had been involved.

After another series of calls, with Angela Merkel of Germany and again with Trump and Britain’s Theresa May, Macron ordered his military to send Rafale warplanes to strike Syria’s chemical weapons facilities.

It was in the “Jupiter” command center of the Elysee palace in the early hours of Saturday morning that the 40-year-old French leader, surrounded by 10 of his diplomatic and defense officials, followed the operation as it unfolded.

Political opponents had criticized Macron for drawing a red line over chemical attacks after the unfortunate precedent set by former U.S. President Barack Obama, who had put himself in a tough spot with a similar ultimatum in 2012.

Obama had to backtrack in the face of congressional opposition, signaling U.S. fatigue in the Middle East and empowering Russia, Western military experts said at the time.

Pointing to the overnight strike, another advisor to Macron said: “This is proof today that the political line he drew at the start of his mandate was meant to be respected.”