President Abdel Fattah al-Sisi inaugurated Egypt's largest church and mosque in the country's New Administrative Capital on Jan. 6, the eve of Coptic Christmas in the predeominantly Muslim country.
The move was a message of tolerance in the predominantly Muslim country, Reuters news agency reported.
"This is an important moment in our history," Sisi said in a speech as he opened the cathedral. "We are one and we will remain one," he added, referring to Egyptian Christians and Muslims.
"On this day we see you have fulfilled this promise and here we are witnessing a great opening on this grand occasion," the head of the Coptic church Pope Tawadros II said. He will preside over midnight mass later in the evening with Sisi in attendance.
Located about 45 kilometers (28 miles) east of Cairo, the cathedral hosted its mass under heavy security, a day after a bomb near a Coptic church in Nasr City, an eastern suburb of Cairo, killed a policeman.
The cathedral can accommodate 8,000 worshippers and the mosque twice as many.
Coptic Christians make up about 10 percent of Egypt's population. More than 100 Copts have been killed in attacks since December 2016.
The head of Al-Azhar, Sheikh Ahmed El-Tayeb said that this was a momentous occasion and "an embodiment of the soul of brotherhood and love."
Pope Tawadros II said: "This is a day of joy as we see our beloved country write a new page in the history of civilization. We pray for our unity to continue as the world witnesses such tolerance and love in our country, God bless you all, long live Egypt."
Copts have in recent years faced a growing number of attacks by Islamist extremists including the group calling itself Islamic State, which is fomenting conflict in the north of the remote Sinai Peninsula.
Among foreign dignitaries and officials were Palestinian President Mahmoud Abbas and Arab League Secretary General Ahmed Aboul Gheit who stood next to Sisi at the opening.
Gheit said that the inauguration of El Fattah El Aleem Mosque and the Nativity of Christ Cathedral in the New Administrative Capital at the same time will be etched in Egypt's history.
He expressed Christmas greetings to Pope Tawadros II of Alexandria and Patriarch of St. Mark Diocese, and said that this demonstrated to the whole world the Egyptians' unity, Egypt Today reported.
Gheit said he is keen on offering Christmas greetings to Pope Tawadros in real appreciation of his great religious and national role.