Egypt's public prosecutor says 48 suspected members of so-called Islamic State (IS) have been referred to a military court in connection with three bombings of Coptic churches.
Thirty-one of the suspects are in custody while the others are still at large.
More than 70 people died in suicide attacks against churches in Cairo in December and in the cities of Tanta and Alexandria in April.
IS said it carried out the bombings.
In a statement on Sunday, public prosecutor Nabil Sadek said some of the suspects were leaders within IS and had formed cells in Cairo and the southern province of Qena to carry out the church attacks.
He said the militants were also responsible for killing eight police officers at a checkpoint in Egypt's Western Desert in January.
The attack in December killed 29 people at Saint Peter and Saint Paul Church in central Cairo, close to the headquarters of Coptic Pope Tawadros II.
In April, 45 worshippers celebrating Palm Sunday died in attacks at St George's Coptic church in Tanta and St Mark's in Alexandria.
IS has threatened more attacks on Egypt's Coptic Christians, who make up 10% of the population.
Egypt's President Abdul Fattah al-Sisi announced a three-month state of emergency after the attacks in April.
What is the Coptic Christian faith?
The Coptic Orthodox Church is the main Christian Church in Egypt. 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. The head of the Church is called the Pope and is considered to be the successor of St Mark.
This makes it one of the earliest Christian groups outside the Holy Land.
The Church separated from other Christian denominations at the Council of Chalcedon (451 AD) in a dispute over the human and divine nature of Jesus Christ.
The early Church suffered persecution under the Roman Empire, and there were intermittent persecutions after Egypt became a Muslim country. Many believe that continues to this day.