U.S. journalist James Foley and three other American hostages were waterboarded during their captivity in Syria by Islamic State militants, The Washington Post reported, citing people familiar with the treatment of Western hostages.

The brutal practice appears to be modeled on the CIA's technique of waterboarding terrorist suspects during interrogations following the Sept. 11 terrorist attacks, mainly popularized after it was used on three captured suspects from Washington and New York.

A source close to the family of a hostage held by Islamic State acknowledged to Reuters that hostages had been waterboarded but provided no further details.

"They knew exactly how it was done," said a person who has direct knowledge of what happened to the hostages and spoke to the Washington Post on the condition of anonymity, adding that Foley and the other captives were held in Raqqa, Syria.

Apart from Foley, who was subsequently beheaded by his captors, three Americans and fewer than  10 other Western hostages are still being held by the militant group, according to people familiar with the situation.

Waterboarding, a form of torture in which subjects are strapped down while water is poured over a cloth covering their face until they feel as if they are suffocating, has been criticized and characterized by many U.S. politicians as torture.

Additionally, President Obama has condemned the practice, and a 2008 op-ed written by Democratic senators Dianne Feinstein of California and Sheldon Whitehouse of Rhode Island criticized this form of coercive interrogation out of fear that militant groups and dictators might attempt to waterboard American captives, UK MailOnline reported.

"Waterboarding dates to the Spanish Inquisition and has been a favorite of dictators through the ages, including Pol Pot and the regime in Burma," the two wrote while supporting an anti-torture bill. "Condoning torture opens the door for our enemies to do the same to captured American troops in the future."

Meanwhile, it was confirmed by a second person that Foley was tortured, including by waterboarding.

"ISIL is a group that routinely crucifies and beheads people," a U.S. official said. "It needs no inspiration for its brutality. To suggest that the U.S. is somehow responsible for ISIL tactics is ridiculous and feeds into their twisted propaganda."

Foley, who was abducted Nov. 22, 2012, was beheaded by Islamic State militants last week in retaliation for U.S. airstrikes against ISIS fighters in Iraq. A graphic video of the killing was posted.

The group is now threatening to execute Steven Sotloff, 31, as well.