The Sunni Islamic State (ISIS/ISIL) has boasted that key U.S. Middle East ally Saudi Arabia is the top provider of terrorists for the jihadist group in Iraq, reports Fox News, citing Iraqi military sources.

Sunni Saudi Arabia shares an estimated 500-mile-long border with war-ravaged Iraq.

Nevertheless, Fox News reports that the Saudi jihadists crossed into Iraq over the border the country shares with both Turkey and Syria.

The news outlet learned from unnamed Iraqi intelligence sources that jihadist from the Saudi kingdom comprise nearly one-third (up to 30 percent) of all ISIS terrorists in Iraq, adding that “Saudis comprise the largest single contingent of ISIS fighters, with Russian Chechens making up the second-largest contingent.”

Speaking to the news outlet on condition of anonymity, a high-ranking Iraqi intelligence officer said, “The Saudi presence in ISIS is very large. What we have left are mainly Iraqis and Saudis.”

“The Saudis make up a large number of suicide bombers, as they already have the ground work of radicalization installed in their minds from radical sheikhs in Saudi [Arabia]. And we’ve caught important ISIS commanders,” he added.

Fox News points out that it has seen various ISIS-linked photographs and documents showing identification and credit cards of Saudi terrorists.

The report comes nearly a month after an article by the Wall Street Journal (WSJ) revealed that President Donald Trump’s administration is considering forming a military alliance with major Middle East allies, including the Sunni Saudi kingdom, to combat Shiite Iran.

President Trump’s anti-Iran coalition would bring together Saudi Arabia, the United Arab Emirates (UAE), Israel, Egypt, and Jordan.

The Sharia law-compliant kingdom Saudi Arabia is regarded as a hotbed and top global exporter of radical Islamic thought, namely the Sunni extremist ideology of Wahhabism, adhered to by ISIS and various other jihadists groups.

Saudi Arabia imposes extremely strict Islamic laws on its citizens.

“Wahhabism was born in Saudi Arabia. Saudi is leading those extremist organizations like ISIS,” an anonymous Iraqi official told Fox News. “They have high-ranking officials and fighters among their ranks. Saudi is nothing without U.S. protection; it is only a bite for Iran to eat.”

Sunni Saudi Arabia considers Shiite Iran its regional rival. Iran exerts tremendous influence over the Shiite-led government of Iraq where militias backed by the Islamic Republic are fighting ISIS.

Saudi Arabia is part of the U.S.-led coalition against ISIS in Iraq and Syria. The Sunni kingdom, which has cracked down on the jihadist group within its borders, has also suffered attacks carried out by ISIS.