The Islamic Center of Fort Pierce, Fla. (St. Lucie County Sheriff’s Office)

The mosque where Pulse nightclub shooter Omar Mateen once worshiped was intentionally set on fire overnight, authorities in Florida said.

The St. Lucie County Sheriff’s Office said emergency crews responded to Islamic Center of Fort Pierce shortly after midnight Monday and extinguished the flames that were spilling out of the mosque.

Authorities are investigating the incident as arson.

“A fire at any place of worship is alarming, regardless of the circumstances,” the sheriff’s office said in a statement. “Video captured at the Fort Pierce Islamic Center shows an individual approached the east side of the building just moments before a flash is seen and the fire starts.”

Sheriff’s officials said they will soon release the video to the public and ask for help identifying the suspect in the arson case.

The fire came at at the beginning of Eid al-Adha, an important Islamic holiday. As The Post’s Pamela Constable noted, the three-day festival “commemorates the willingness of Ibrahim, the figure known as Abraham in the Bible, to follow God’s command to sacrifice his son Ishmael, who was later saved by an angel and lived to be 137.” The holiday is not to be confused with Eid al-Fitr, a separate festival that marks the end of Ramadan.

An undated photo from a social media account of Omar Mateen. (Myspace via Reuters)

The Islamic Center of Fort Pierce had an Eid prayer scheduled for 9 a.m. Monday. Those who intended to worship were instructed to go to another mosque in the area.

“It is with a very heavy heart that we have to announce that last night around midnight, there was an arson attack on our Mosque,” the Islamic Center said a statement early Monday. “Please keep us in your Du’as and prayers.”

Early Monday, Maj. David Thompson with the St. Lucie County Sheriff’s Office told reporters it was a “horrible tragedy not only for the Islamic center but for our community.”

“I don’t want to speculate on a motive,” he said. “We all know the implications of the date and the time of year that this is — the 9/11 anniversary. Is that related? I wouldn’t want to speculate, but certainly that is in the back of our minds.”

The mosque became a locus of attention in June, after Mateen opened fire at a gay nightclub in Orlando, killing 49 people and leaving dozens of others injured. Mateen himself was killed in a shootout with police inside Pulse.

Mateen occasionally attended the Islamic Center of Fort Pierce, coming to prayers with his father and young son, Imam Shafiq Rahman told The Post in June. Mateen’s three sisters were active volunteers at the mosque, which has about 150 congregants.

“He was the most quiet guy — he never talked to anyone,” Rahman said days after the Orlando massacre. “He would come and pray and leave.”

As The Post’s Mary Jordan previously reported, Mateen was at the mosque just two days before the deadly shooting spree. On that evening, a Friday, “he knelt for over an hour on the green carpet of the Fort Pierce mosque, praying with his young son.”

The first American to carry out a suicide bombing in Syria, Moner Mohammad Abusalha, also occasionally worshiped here before he left his car outside the mosque in 2014, flew to Syria, burned his U.S. passport and blew himself up in an operation for an al-Qaeda affiliate.

The FBI looked for a potential connection between Mateen and Abusalha in 2014 and did not find “ties of any consequence,” aside from the two men knowing each other “casually” from attending the same mosque, said the bureau’s director, James B. Comey, on Monday.

But in the wake of Sunday’s attack in Orlando, there is a new focus on this small working-class town in South Florida and the mosque atttended by two of the most infamous Muslim extremists with U.S. roots.

The Islamic Center of Fort Pierce on June 12. (Ben Fox/AP file)

Ibrahim Hooper, spokesman for the Council on American-Islamic Relations, said attacks against the American Muslim community are becoming a daily occurrence in America since Islamophobia moved into the mainstream.

“Unfortunately, within the past year, we’ve seen an unprecedented rise in bigotry in our society,” Hooper said Monday, adding: “It’s becoming a great concern to the American Muslim community.”

Hooper said it is up to the majority that does not hold anti-Islamic views to stand up and say so.

He said Muslims feel “under siege like never before in our history” and need support from others to push back against “all the voices of hate.”