Egypt's President Abdel Fattah al-Sisi said a three-month state of emergency will be imposed after two deadly bombings hit Coptic churches, killing at least 44 people.
"A series of steps will be taken, most importantly, the announcement of a state of emergency for three months after legal and constitution steps are taken," Mr Sisi said in a speech aired on state television.
The so-called Islamic State claimed responsibility for the attacks, which also injured more than 100 people and occurred a week before Coptic Easter, with Pope Francis scheduled to visit Egypt later this month.
The first bombing, in Tanta, a Nile Delta city about 100km north of Cairo, tore through the inside of St George Church during its Palm Sunday service, killing at least 27 people and injuring at least 78, the Ministry of Health said.
The second, carried out a few hours later by a suicide bomber in Alexandria, hit Saint Mark's Cathedral, the historic seat of the Coptic Pope, killing 17 people, including three police officers, and injuring 41, the ministry added.
Coptic Pope Tawadros, who had attended mass at Saint Mark's Cathedral, was still in the building at the time of the explosion but was not harmed, the Interior Ministry said.
"These acts will not harm the unity and cohesion of the people," Pope Tawadros said later, according to state media.
President Abdel Fattah al-Sisi condemned the attacks and summoned the National Defence Council to an urgent session.
Deflecting Western criticism that he has suppressed political opposition and human rights activists since he won election in 2014, Mr Sisi has sought to present himself as an indispensable bulwark against terrorism in the Middle East, and he identifies militant Islam as a threat.
"The attack ... will only harden the determination (of the Egyptian people) to move forward on their trajectory to realise security, stability and comprehensive development," Mr Sisi said in a statement.
Thousands gathered outside the Tanta church shortly after the blast, some weeping and wearing black.
"There was a huge explosion in the hall. Fire and smoke filled the room and the injuries were extremely severe," a Christian woman, Vivian Fareeg, said.
Islamic State's branch in Egypt appears to be stepping up attacks and threats against Christians, who comprise about 10 percent of Egypt's 90 million people and amount to the biggest Christian minority in the Middle East.
In February, scores of Christian families and students fled Egypt's North Sinai province after a spate of targeted killings.
Those attacks followed one of the deadliest on Egypt's Christian minority, when a suicide bomber hit its largest Coptic cathedral, killing at least 25 people. IS later claimed responsibility for that attack.
IS has waged a low-level war against soldiers and police in Egypt's Sinai Peninsula for years. It now seems to be changing tactics, targeting Christian civilians and broadening its reach into Egypt's mainland. That is a potential turning point in a country trying to prevent a provincial insurgency from spiralling into wider sectarian bloodshed.