Reuters was not able to verify the authenticity of the video but the killings were similar to past violence carried out by Islamic State, which has expanded its reach from strongholds in Iraq and Syria to chaotic Libya.
The video portrayed Christians as crusaders out to kill Muslims and then showed about 15 men beheaded on a beach and another group of the same size shot in their heads in scrubland.
Egyptian President Abdel Fattah al-Sisi ordered air strikes on Islamic State targets in February in Libya after the group posted a video of militants beheading 21 Egyptian Christians.
"Muslim blood shed under the hands of your religions is not cheap," he says, looking at the camera. "To the nation of the cross we are now back again."