The mastermind behind the Paris terror attacks was identified Monday as an ISIS fighter from Belgium who is also tied to the recent failed attack on a high-speed European train and a plot against a French church.

Abdelhamid Abaaoud, 27, grew up the child of Moroccan immigrants in Brussels’ Molenbeek district — infamous as a hotbed of Islamic extremism — before joining ISIS and embracing its war against the West.

“All my life, I have seen the blood of Muslims flow,” he said in a 2014 video. “I pray that Allah will break the backs of those who oppose him, his soldiers and admirers, and that he will exterminate them.”

Abaaoud even convinced his then-13-year-old brother, Younes, to join him in Syria, where the teen became one of ISIS’s youngest fighters and was featured in the terror group’s propaganda magazine, Dabiq.

Grisly photos and videos from Syria also show Abaaoud and fellow ISIS fighters loading bloody corpses onto a pickup truck.

“Before we towed Jet Skis, motorcycles, quad bikes, big trailers filled with gifts for vacation in Morocco,” he says into the camera in one video. “Now, thank God, following God’s path, we’re towing apostates, infidels who are fighting us.”

A French official said Abaaoud was tied to the August attack on a Paris-bound train that was foiled by three Americans, as well as another failed plan to target a suburban church outside the French capital.

Belgian authorities also suspect him of organizing a terror cell that was crushed during a Jan. 15 shootout in Verviers, where cops killed two plotters.

Afterward, Abaaoud claimed he had been leading the group inside Belgium but slipped through a police dragnet and escaped back to Syria.

“I was even stopped by an officer who contemplated me so as to compare me to the picture, but he let me go, as he did not see the resemblance!” he boasted in an interview.

Meanwhile, the brother of two Paris attackers — one of whom blew himself up with a suicide vest, while the other is on the run — was released from custody in Belgium and denied any knowledge of his kin’s deeds.

“We don’t know what has happened to Ibrahim and Saleh,” Mohammed Abdeslam told reporters. “I found out about it on the TV like everyone else.”

Also Monday, French officials identified two more of Friday’s attackers, including Samy Amimour, 28, who blew himself up during the siege at the Bataclan theater.

In 2013, Amimour’s father, Mohamed, traveled to Syria to try to persuade his son to quit ISIS by bringing a letter from his mom.

But their reunion was supervised by an ISIS thug “who never left us alone,” Mohamed told the French paper Le Monde last year, and Samy ignored his father’s desperate pleas.

With Post wire services