A still from the video released by ISIS Sunday, showing the Egyptian Christians killed by the group in Libya.

Egypt's air force launched airstrikes against ISIS targets in Libya overnight, in reaction to a grisly video released by ISIS Sunday showing the group beheading Egyptian Coptic Christians it had held hostage in Libya for weeks.

The video shocked many in Egypt, and spurred calls for the government to take action. In a late-night televised address Sunday, President Abdel Fattah el-Sisi promised that Egypt would respond.

"These cowardly actions will not undermine our determination," said Sisi, who also banned all travel to Libya by Egyptian citizens. "Egypt and the whole world are in a fierce battle with extremist groups carrying extremist ideology and sharing the same goals."

A spokesman for Egypt's military announced the airstrikes on state television Monday morning, the first time Egypt has acknowledged taking foreign military action since it fought in the Persian Gulf War in 1991.

"Let those far and near know that Egyptians have a shield that protects them," read the statement.