Several videos showing a man believed to be Yasuda have been also released in the past year.
Yasuda started reporting on the Middle East in early 2000s. He was taken hostage in Iraq in 2004 with three other Japanese, but was freed after Islamic clerics negotiated his release.
His most recent trip to Syria was in 2015 to report on his journalist friend Kenji Goto, who was taken hostage and killed by Daesh, also known as ISIS or ISIL.
Contact was lost with Yasuda after a message to another Japanese freelancer on June 23, 2015. In his last tweet two days earlier, Yasuda said his reporting was often obstructed and that he would stop tweeting his whereabouts and activities.