The families of Alan Henning, a British aid worker believed to have been beheaded by the Islamic State group, and Peter Kassig, a U.S. national being held hostage by the militant group formerly known as either ISIL or ISIS, issued statements in the wake of its Henning execution video, which was released Friday.

“Alan, my husband, and father of Lucy and Adam, was kidnapped in Syria in December last year. Last night, we received news of his murder by ISIL. It is the news we hoped we would never hear. As a family, we are devastated by the news of his death. There are few words to describe how we feel at this moment. Myself, Lucy and Adam, and all of Alan’s family and friends are numb with grief,” the Henning family said in its statement Saturday.

World leaders condemned the murder of Henning, calling the act by the Islamic State group “barbaric” and “cowardly.” The video purporting to show the beheading was described by the militant group as “another message to America and its allies,” after recent coalition airstrikes on its assets in the Middle East.

In the video, the apparent executioner warned U.S. President Barack Obama against continuing airstrikes in Syria. If the airstrikes do not stop, the group member indicated, then former U.S. Army Ranger Peter Edward Kassig would be the next Islamic State victim.

Kassig’s parents released a video Saturday pleading for their son’s safe return. In it, Edward and Paula Kassig discuss their son’s charitable efforts in Syria before he was taken captive Oct. 1, 2013. Kassig is now known as Abdul-Rahman Kassig, having converted to Islam while in captivity.

“As Muslims around the world, including our son Abdul-Rahman Kassig, celebrate Eid ul-Adha, the faith and sacrifice of Ibrahim, and the mercy of Allah, we appeal to those holding our son to show the same mercy and set him free,” the family said in a statement posted on a Facebook page dedicated to their son.

In the video, Paula Kassig mentions receiving messages from her son this year, including word of an unidentified friend who was captured at the same time as Kassig. “We know you were very worried about your friend who was taken with you. He was released and is well.”

In concluding the video, Paula Kassig says, “We implore those who are holding you to show mercy and use their power to let you go.”