President Abdel Fattah El Sisi inaugurated Egypt's largest church and mosque in the country's New Administrative Capital on Sunday, the eve of Coptic Christmas, in a message of tolerance in the predominantly Muslim country.
It came a day after a deadly bomb blast near a church in the country where militants have repeatedly targeted Christians.
Copts, the largest Christian minority in the Middle East, were due hold a midnight Mass in the Cathedral of the Nativity, billed by the government as the Middle East's largest church, a few hours after the official opening.
Coptic Christians make up an estimated 10 per cent of Egypt's nearly 100 million people. .
They have increasingly been targeted in recent years by Islamist militants, including ISIS, which is waging an insurgency in the north of the remote Sinai Peninsula.
Foreign dignitaries and officials including Palestinian President Mahmoud Abbas and Arab League Secretary General Ahmed Aboul Gheit flanked Mr Sisi at the opening, state television showed.
Angham, a prominent local singer, sang for Muslim-Christian coexistence as a display of fireworks lit the skies over the two houses of worship.
"This is an important moment in our history," Mr Sisi said in a speech as he opened the cathedral. "We are one and we will remain one," he said, 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 with Mr Sisi in attendance.
US President Donald Trump also praised the opening of the church and the mosque.
"Excited to see our friends in Egypt opening the biggest Cathedral in the Middle East. President Sisi is moving his country to a more inclusive future," Mr Trump tweeted on Sunday.
The Cathedral of the Nativity, adorned with Coptic icons, can accommodate more than 8,000 worshippers while Al Fattah Al Aleem Mosque can hold nearly double that number. Both are located in the new administrative capital, a major development located about 45 kilometres east of Cairo.
Sheikh Ahmed Al Tayeb, Grand Imam of the Al Azhar Mosque, said Islam obliges Muslims to safeguard and defend houses of worship, whether Muslim, Christian or Jewish.
Contractors have been clearing debris from the perimeter of the cathedral in the last two weeks in preparation for the inauguration.
The new Egyptian capital, announced in March 2015, is intended partly to reduce crowding in Cairo but will also be home to government ministries and an airport. The government is expecting to begin moving to the new premises this year.