(Reuters) - Islamic State released a video on Sunday purporting to show the militant group beheading 21 Egyptian Christians kidnapped in Libya.

In the video, militants in black marched the captives, dressed in orange jump suits, to a beach. They were forced down onto their knees, then beheaded. The video appeared on the Twitter feed of a website that supports Islamic State.

A caption on the five-minute video read: "The people of the cross, followers of the hostile Egyptian church."

Thousands of Egyptians have traveled to neighboring Libya in search of jobs since an uprising at home in 2011, despite advice from their government not to go to one of the most dangerous countries in the region.

Before the killings, one of the militants stood with a knife in his hand and said: "Safety for you crusaders is something you can only wish for."

(Reporting by Ahmed Tolba; Writing by Michael Georgy; Editing by Kevin Liffey)