Egyptian authorities must protect churches and Christian homes and businesses from attack and Islamists must stop inciting sectarian violence, Human Rights Watch said on Thursday.
The group said it had documented attacks on 42 churches and dozens of Christian institutions, schools and homes, as well as Christian-owned businesses across the country.
It said at least four people were reported killed in sectarian violence, three Christians and one Muslim.
Attacks on Egypt's Christian minority have escalated since the July 3 ouster of Islamist president Mohamed Morsi.
The attacks dramatically increased since the August 14 dispersal of two pro-Morsi protest camps in the capital.
Human Rights Watch said authorities had failed to protect Christians from attacks, and that Islamists, including Morsi's Muslim Brotherhood, had failed to properly condemn the violence and prevent future attacks.
"For weeks, everyone could see these attacks were coming, with Muslim Brotherhood members accusing Coptic Christians of a role in Mohamed Morsi's ouster, but the authorities did little or nothing to prevent them," said Joe Stork, the group's acting Middle East director.
"In the vast majority of the 42 cases Human Rights Watch documented, neither the police nor the military were present at the start or during the attack," the group said.
It said a priest in Minya province told the group he had called police and emergency services multiple times as mobs attacked his church, but no one came.
A bishop told the group he contacted senior government officials to plead for help, and though they promised to send protection, none arrived.
But while HRW criticised the government for failing to protect Christians, it also said the country's Islamists deserved blame for inciting the attacks.
They came "after weeks of sectarian discourse by Muslim Brotherhood supporters" at two pro-Morsi protest camps, the group said.
And while some Muslim Brotherhood leaders have condemned the attacks, others "have suggested a Coptic role in the ongoing crackdown on the group," HRW said.
"While a few Muslim Brotherhood leaders have condemned these attacks, they also need to tell the group's followers to stop inciting violence by insinuating that the Coptic minority is responsible for the crackdown," Stork said.
Copts make up about 10 percent of Egypt's population, and are the largest Christian denomination in the country.
However, there are also Roman Catholics, Anglicans, Chaldeans, Greek Catholics, Orthodox and various Protestant groups present in the country. Some of them also suffered attacks on their churches or church-related institutions.