Coptic lady horrified by the Cairo cathedral bombing last December.

ISIS published a video on Sunday threatening Egyptian Christians and showing the last statement of a man it said was responsible for the deadly bombing in December of a Coptic cathedral in Cairo.

The masked man in battle-dress, whom the group identified as Abu Abdallah al-Masri, is seen encouraging militants all over the world not to give up and promising Islamists jailed in Egypt they will be freed soon, when the group “liberates” Cairo.

President Abdel Fattah al-Sisi had already identified the bomber as a 22-year-old student called Mahmoud Shafik, and it is believed Abu Abdallah al-Masri was his assumed name. He had been detained for two months in 2014 before joining an ISIS cell in Sinai, the government said.

“Finally, to my brothers in captivity: rejoice, you believers, do not falter or grieve. I swear to God we will very soon liberate Cairo and free you from captivity. We will come bearing explosives, I swear we will, so rejoice you believers,” he said in the video.

At least 28 people, mostly women and children, were killed in December when a bomb exploded in a chapel adjoining St Mark’s Cathedral, the seat of the Coptic papacy.

Orthodox Copts, who comprise about 10 percent of Egypt’s 90 million people, are the Middle East’s largest Christian community.

ISIS claimed responsibility for the bombing, its deadliest attack in Egypt outside the Sinai Peninsula, where it has been waging an insurgency since 2013.

The Cairo attack, coupled with the group’s use of a new “IS in Egypt” logo as opposed to “Sinai Province”, suggests an expansion of operations to the rest of the country.