Isis on Saturday (27 May) claimed responsibility for the attack on a bus in Egypt that killed 29 people.
Egypt responded to Friday's attack by launching a series of airstrikes that targeted what it said were militant bases in eastern Libya in which the assailants were trained.
The Egyptian military said on its official Facebook page that the airstrikes were continuing "day and night" and that they have "completely" destroyed their targets.
"What you've seen today will not go unpunished," President Abdel-Fattah el-Sissi said in a televised address late on Friday. "An extremely painful strike has been dealt to the bases.
"Egypt will never hesitate to strike terror bases anywhere."
He said the attacks on Christians aimed at driving a wedge between them and the country's Muslim majority. El-Sisi also appealed to US President Donald Trump to lead the global war against terror.
The claim of responsibility for the terror attack, published by the group's Ammaq news agency, takes the number of deadly attacks targeting Christians to four since December.
Isis claimed the death toll was 32, but there was no immediate explanation for the discrepancy.
El-Sissi declared a three-month state of emergency following April's twin attacks, which fell on Palm Sunday.
The Egyptian cabinet, meanwhile, said 13 victims of Friday's bloodshed remained in hospital in Cairo and Minya province, where the attack took place. The bloodshed came on the eve of the start of the Muslim holy month of Ramadan.
El-Sissi told Pope Tawadros II, spiritual leader of Egypt's Coptic Orthodox Church, in a phone call late on Friday that his government would not rest until the perpetrators of the attack were punished.
After a visit to Egypt last month by Pope Francis, Isis vowed to escalate attacks against Christians and urged Muslims to steer clear of Christian gatherings and Western embassies.