Security forces also discover two farms used to make explosives and store weapons
Egyptian authorities arrested 13 suspected "terrorists" allegedly planning to attack Christians and public institutions, the interior ministry said on Sunday, a week after two deadly church bombings.
The announcement came as Egypt's Christians marked Easter under tight security a week after Palm Sunday bombings claimed by the Islamic State (IS) group killed 45 people at churches in the cities of Tanta and Alexandria.
The "13 terrorist elements" belonged to cells preparing attacks against "government and Christian institutions" and police in four northern provinces, including Alexandria, a ministry statement said.
It was not immediately clear when the arrests took place.
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Security forces also discovered two farms in Alexandria and the neighbouring province of Beheira that were used to make explosives and store weapons, the ministry added.
Egypt's Coptic Church said on Wednesday that it would cut back on Easter celebrations to a simple mass in the wake of the bombings.
Parliament on Tuesday unanimously approved a three-month state of emergency declared by President Abdel Fattah al-Sisi in the aftermath of the attacks.
Copts, who make up about one-tenth of Egypt's population of more than 92 million, have been targeted several times in recent months.
In December, an IS-claimed church bombing in Cairo killed 29 people.
The militant group has threatened more attacks against Egypt's Christian minority.
Last week's bombings came ahead of Roman Catholic Pope Francis's first trip to Egypt, which a Vatican official has said will go ahead as planned on 28 and 29 April 28 in spite of the attacks.