AKIPRESS.COM - An American-born journalist and her mother, who were active in opposition to the Syrian regime, were found murdered in Istanbul, ABC NEWS said. 

Halla Barakat and her mother Orouba Barakat were Syrians living in Turkey and close friends of American humanitarian aid worker Kayla Mueller, who was taken hostage by ISIS in Aleppo, Syria in 2013 and killed 18 months later.

Turkish media reports and sources said the Barakats were strangled and stabbed to death, possibly four or five days ago, then doused in a chemical to delay decomposition. Police officials told ABC News that they are investigating but have made no arrests and have no suspects.

Other sources said the Assad regime is a prime suspect in the killings of the Barakat women.

The women had recounted in "The Girl Left Behind" on ABC's "20/20" last year how they had befriended and worked with Kayla Mueller of Prescott, Arizona, to aid Syrian refugee mothers and their children in Antakya, Turkey, who had fled the civil war in their homeland only a few kilometers away.

"Just saying Kayla's name in front of them, they smile," Orouba Barakat told ABC's Brian Ross in an interview about Mueller.

The FBI has legal jurisdiction to open a case and investigate the killing or kidnapping of American citizens overseas. Officials at the Bureau, however, declined to comment on the death of Halla Barakat on Friday.

The US State Department released a statement condemning the murders and saying officials will "closely follow the investigation," using alternative spellings for the victims' names.