An explosion near the Mar Girgis Coptic Church in the Nile Delta city of Tanta in Egypt has killed 26 people and left 70 others injured, reports Egypt's state television.
A second explosion occurred at Saint Mark's Church in the city of Alexandria, just north of Tanta. Local media have reported 11 deaths and injuring 35 people.
The Foreign Office reported there were four explosions across Egypt and have advised against all but essential travel to the area west of Nile Valley and Nile Delta.
The attacks fell on the celebration of Palm Sunday, which marks the beginning of the Christian festival of Holy Week, which ends on Easter Sunday.
Isis have claimed responsibility for both attacks on the Coptic churches.
The attacks are the latest in a series that began late 2016 when 25 people died and 49 were wounded in a blast at Cairo's largest Coptic cathedral. An Isis affiliate said it was behind that attack.
However, the explosion on 1 April was claimed by a militant group called Liwa al-Thawra, a splinter group of the banned Muslim Brotherhood, leading to suspicions the same organisation could be behind this latest attack.
The incidents have rocked the area just days after another detonation near a police training centre left one policeman dead and 13 injured, weeks before Pope Francis, who has condemned the recent attack, is due to visit to Egypt.
Francis sent his "deep condolences to my brother, Pope Tawadros II, the Coptic church and all of the dear Egyptian nation". Pope Tawadros II is the leader of the Coptic Orthodox Church of Alexandria.
He continued, asking God to "convert the hearts of those who spread terror, violence and death, and also the hearts of those who make, and traffic in, weapons".
Egypt's Coptic Christian community, who make up 10% of the country's 85 million population, have been singled out for attacks by Islamist terrorists, including Muslim Brotherhood splinter groups and Isis, since the military overthrew elected president Mohammed Morsi in 2013. Pro-Morsi terrorists blame Christians for supporting the coup.
CBC TV published footage of the scenes inside the church, showing blood and corpses on the floor and survivors flocking to cover the bodies in respect of the dead.