Egypt's top security official says Gaza militants were to blame for the deadly suicide bombing outside a Coptic Christian church on New Year's Day.
Interior Minister Habib al-Adly said conclusive evidence showed the shadowy Army of Islam in the Palestinian territory was behind the planning and execution of the attack, which killed 21 people and sparked three days of Christian rioting in Cairo and several other cities.
It was the deadliest attack against Christians in Egypt in more than a decade. About 10 percent of Egypt's 80 million people are Christians.
The Army of Islam dismissed Sunday's accusations on an extremist website.
"The Army of Islam in the land of Ribat denies the allegation made by the Egyptian regime about our relation with the attack in the city of Alexandria," it said in an Internet posting.
Al-Adly said the group is believed to have recruited Egyptians in the planning and execution of the attack, but that this could not conceal the role it played in the "callous and terrorist" act.
Security officials said earlier on Sunday that at least five Egyptians have been detained in connection with the Alexandria bombing. They said the suspects have given investigators a full account of how they were contacted and eventually recruited by the Army of Islam.
The Army of Islam is estimated to have several dozen operatives committed, like al-Qaeda, to the ideas of a global jihad.