ISIS Twists Emotional Knife With New Hostage Messages

Cruel pleas by U.S., British hostages blame leaders, not terrorists, for deaths.

WASHINGTON — -- The extremists in Syria and Iraq who've publicized their gruesome decapitations of four American and British hostages released new messages Sunday from one of the men they murdered as well as from another hostage who has said he may soon suffer the same fate.

"To Mom, I do not have much time and will probably not get this opportunity again, so I would like to get straight to the point. Your recent public video of pleading to the Caliphate not to kill me has been received loud and clear by them. However, this in itself is not enough to save me," began a purported message from American journalist Steven Sotloff, apparently composed before he was beheaded by a masked British killer in a video posted online on Sept. 2.

The full text of Steven Sotloff's purported letter to his mother was published by ISIS in its online magazine Dabiq, released on Sunday.

A Sotloff family representative didn't immediately respond to a request for comment on the "letter" published by ISIS or its authenticity.

The parents of another American hostage who ISIS has said may be executed next, former Army Ranger Abdul-Rahman Kassig, made pleas to al-Baghdadi to spare their son in tweets late last week as well as during a prayer vigil Friday at the Islamic Society of North America in Indianapolis. Paula and Ed Kassig said their son, formerly known as Peter, had converted to Islam while in captivity.

The cruelly agonizing letter by Sotloff -- very likely written not by him but by his murderers, officials said -- insisted that his fate would be determined by President Obama's "next judgment," and said his mother "can still save my life" by not letting the American leader "get away with murder again." The solution was simple, Sotloff's letter argued: "Leave them [ISIS] to fight their own war."

Meanwhile, ISIS released the latest in a series of "programs" by another hostage, British freelance journalist John Cantlie, who officials believe has been forced by his captors to blame the U.K. government for the video beheadings of his former cellmates.

The beheading videos made in Syria's desert landscape have come in a cycle of every two weeks, but have more recently shown less of the local terrain to frustrate intelligence services.

Cantlie quoted military blog "War On The Rocks," New York Times columnist Thomas Friedman and Obama about the difficulty of fighting ISIS, as well as outspoken former CIA Osama Bin Laden hunter Michael Scheuer. Appearing to read from a TelePrompTer, Cantlie blandly delivered the terrorists' dare for the West to inject ground forces into the fight now being waged only with daily air strikes.

ABC News' Alex Hosenball contributed to this report.