Somali Islamic extremists beheaded four Christians after kidnapping them on July 27, according to a report from the group, International Christian Concern.
The four worked for an organization that has been helping orphans in southern Somalia.
A spokesman for Al-Shabab said the four were guilty of abandoning Islam.
An eyewitness told the ICC that the four were given the chance to renounce their faith in Jesus Christ and embrace Islam. But they refused, even though the terrorists promised to release them.
Al-Shabab has been waging war against the small Christian population in Somalia. It is seeking to overthrow the government and establish an Islamic state in Somalia.