The terror group said that it was behind the hideous bomb atacks which caused carnage at two seperate Coptic churches on Palm Sunday.
ISIS has launched a fresh campaign of terror in the latest assault on a religious minority increasingly targeted by Islamist militants.
The first bombing, in Tanta, a Nile Delta city less than 100 kilometres outside Cairo, killed at least 27 and injured at least 78, Egypt's Ministry of Health said.
The bombings come as Islamic State's branch in Egypt appears to be stepping up attacks
The second, carried out just a few hours later by a suicide bomber in Alexandria, hit the historic seat of the Coptic Pope, killing 17, including three police officers, and injuring at least 48, the ministry added.
The bombings come as Islamic State's branch in Egypt appears to be stepping up attacks and threats against Christians.
Pope Tawadros, who had attended mass at Saint Mark's Cathedral, was still in the building at the time of the explosion but was not harmed, the Ministry of Interior said.
A man stands over one of the victims who died in the blast in Tanta Egypt
Thousands gathered outside the church in Tanta shortly after the blast, some wearing black, crying, and describing a scene of carnage.
"There was blood all over the floor and body parts scattered," said a Christian woman who was inside the church.
"There was a huge explosion in the hall. Fire and smoke filled the room and the injuries were extremely severe," another Christian woman, Vivian Fareeg, said.
President Abdel Fattah al-Sisi and Prime Minister Sherif Ismail are set to visit the Tanta site on Sunday and Sisi has ordered an emergency national defence council meeting, state news reported.
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At least 11 people were killed in the blast in Alexandria
Egypt's Christian community has felt increasingly insecure since Islamic State spread through Iraq and Syria in 2014, ruthlessly targeting religious minorities.
In 2015, 21 Egyptian Christians working in Libya were killed by Islamic State.
Copts face regular attacks by Muslim neighbours, who burn their homes and churches in poor rural areas, usually in anger over an inter-faith romance or the construction of a church.
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