Egyptian President Abdel Fattah al-Sisi has announced a three-month state of emergency after bombings at two Coptic churches on Palm Sunday just weeks before a planned visit by Pope Francis.
The attacks are the deadliest attacks on the Coptic minority in recent memory, news agencies report.
Sisi ordered military troops to be deployed across the country following the attacks.
In a statement, his office said the he had "ordered units from the military to immediately deploy and assist the civilian police in securing vital facilities in all provinces of the republic".
The president, who will have to present his state of emergency decision to parliament within a week, has warned that the war against Isis militants "will be long and painful".
The first bombing happened at the Mar Girgis church in Tanta city, north of Cairo. Twenty-seven people were killed, the health ministry confirmed.
A second blast hit St Mark's Church in Alexandria where the Coptic Pope Tawadross II was leading the Palm Sunday service. Palm Sunday is observed a week before Easter Sunday, and is one of the holiest days in the Christian calendar as it marks Jesus's entry into Jerusalem before his crucifixion.
Pope Tawadross escaped unharmed.
That explosion killed 17 people, including at least four police officers who had tried to stop the suicide bomber from entering the church.
State television reported claim that the interior minister had sacked the provincial head of security after the attacks.
Coptic churches targeted before
Egypt's Coptic Christians have been the target of attacks since the ousting of the former president Mohamed Morsi in 2013.
Militants and Islamists believe the Copts had supported the military overthrow of the Islamist president. In December 2016, 29 worshippers at a Cairo church were killed by Isis.
In 2011, a Coptic church in the coastal city of Alexandria was bombed on New Year's Day killing more than 20 people.