The main difference from other execution videos it has released is that the new one appears to have taken place on the southern shore of the Mediterranean, on a rocky beach said to be in western Libya, far closer to Europe than sites previously depicted.

Fighters under the banner of the Tripolitania Province of the Islamic State announced last month that they were holding about 20 Egyptian Christians, or Copts. A similar number of Egyptian Christians in Libya seeking work had disappeared in the mid-coastal city of Surt. Officials of both the Egyptian government and the Coptic Church confirmed that captives seen in a photograph with the announcement were the missing Egyptian Christians, and on Sunday confirmed that they were killed in the video.

In the video, masked fighters identified as from the Tripolitania Province of the Islamic State, dressed in black with machetes at their chests, parade along a rocky beach toward the camera with a row of bound captives in orange jumpsuits, like the ones worn by victims in previous Islamic State videos.

About five minutes long, the video bears the logo of Al Hayat, the Islamic State’s media arm. Unlike the cellphone videos usually made by Libyan militants, it is as polished as previous Islamic State videos, with slow motion, aerial footage and the quick cuts of a music video. The only sound in much of the background is the lapping of waves.

The captives are made to kneel in the sand. Then they are simultaneously beheaded with the theatrical brutality that has become the trademark of Islamic State extremists. There was no indication in the video about when the beheadings took place.

The lead executioner speaks in fluent English with an American accent, and his words are translated in Arabic subtitles. Under the title “A Message Signed With Blood to the Nation of the Cross,” he emphasizes that the fighters are just one part of the broader Islamic State group.

“Oh, people, recently you have seen us on the hills of as-Sham and Dabiq’s plain, chopping off the heads that have been carrying the cross for a long time,” he said, using Arabic terms for places in and around Syria. “Today, we are on the south of Rome, on the land of Islam, Libya, sending another message.”