International media outlets report that a bomb explosion in the Coptic Christian cathedral complex in the Egyptian capital Cairo has killed at least 25 people, officials say.

Dozens of others were injured in the blast in a chapel adjoining St Mark's cathedral during a Sunday service.

Citing Egyptian state media, The New York Times reports the explosion killed at least 25 people and wounded 49, mostly women and children.

One of witnesses told the Associated Press news agency that many of the victims were women and children.

There was no immediate claim of responsibility, although the attack bore the hallmark of Islamist militants fighting President Abdel Fattah el-Sisi who have previously targeted minority Christians over their perceived support for his government

Egypt has seen a wave of attacks by militants since 2013 when the military overthrew President Mohammed Morsi, an elected leader who hailed from the Muslim Brotherhood, and launched a crackdown against Islamists.

Some of Mr. Morsi's supporters blamed Christians for supporting the overthrow, according to BBC.

President Abdul Fattah al-Sisi has declared a three-day period of national mourning.

In a statement, he condemned the attack, calling for the perpetrators to be hunted down and punished.

The Coptic Orthodox Church is the main Christian Church in Egypt. Egypt’s Coptic minority reportedly makes up about one-tenth of the country’s roughly 90 million people.  While most Copts live in Egypt, the Church has about a million members outside the country.

Copts believe that their Church dates back to around 50 AD, when the Apostle Mark is said to have visited Egypt. Mark is regarded as the first Pope of Alexandria - the head of their church.  This makes it one of the earliest Christian groups outside the Holy Land.