CAIRO, Dec 11 (Aswat Masriya) - Egypt's presidency has condemned an explosion in the vicinity of the Coptic Orthodox Cathedral and announced three days mourning starting Sunday.  

At least 25 people were killed and tens were injured in an explosion that hit St Peter's church building, which is attached to St Mark's cathedral.

"This treacherous terrorism targets the Copts and Muslims and that Egypt will, as usual, become stronger and more coherent in the face of these circumstances," Egypt's president Abdel Fattah al-Sisi said in a statement. 

Sisi also pledged retribution for victims of the explosion. 

He added that the attack on the church as well as Friday's attack in Haram district in Giza that left six security personnel killed are "part of Egypt's war against terrorism".

Militants have stepped up attacks targeting security forces in Egypt, since the ouster of Islamist President Mohamed Mursi in July 2013 after mass protests against his rule.