CAIRO — A bomb ripped through Cairo’s Coptic cathedral complex during Sunday Mass, killing at least 25 people and injuring 49 and delivering the bloodiest single attack on Egypt’s Christian minority in recent years, according to Egyptian officials and Christian community leaders.

The explosion unfolded inside the 100-year-old Botrosiya Church, also known as the Church of St. Peter and St. Paul, after the 200 or so worshippers had stopped reading verses of the Bible and the priest was getting to ready to start his sermon, witnesses said.

Around 9:45 a.m., “everything turned black suddenly,” recalled Qelliny Farag.

As of Sunday evening, there had been no claims of responsibility. But suspicion fell on Islamic extremists, including Egypt’s Islamic State branch, who have staged numerous attacks across the country this year targeting soldiers, police and government officials. Sunday’s carnage came less than 48 hours after a bomb killed six policemen and injured another three on a road leading to Egypt’s Great Pyramids complex.

The bombing came on a public holiday here, commemorating the birthday of the Prophet Muhammad. Though that is a Muslim celebration, the church was filled with more than the usual number of congregants taking advantage of the day off.

When the bomb detonated, Farag, 80, was seated on the left side of the church. His wife, Samiha Tawfik, was on the right side, along with the other female congregants.

“I could not see anything,” recalled Farag. “We were all in shock, covered in dust, running through corpses that got thrown by the intensity of the blast.”

Unable to breathe from the dust, his head pounding, he stumbled around the pews. Soon, he began to see, and understand, what had happened.

“A minute passed by and I started to see flesh scattered everywhere around us,” he said. “Even the ceiling had collapsed.”

He couldn’t find his wife.

Egypt’s Orthodox Coptic Christian community, which makes up 10 percent of the population, has long felt discrimination at the hands of the country’s Muslims, as well as successive secular but authoritarian rgeimes. And attacks on Christians have intensified since the 2011 populist revolt that ousted President Hosni Mubarak. At least 26 sectarian assaults have targeted the community this year alone, according to human rights activists.

But Sunday’s bombing was the gravest sectarian attack on Christians in recent years. St. Peter’s Church is located inside the St. Mark’s Coptic Orthodox Cathedral complex in the heart of Cairo. The cathedral houses the headquarters of the Coptic Orthodox Church in Egypt, as well as the home of its leader, Pope Tawadros II.

Over the past six years, numerous attacks on Christians have left scores dead. On Jan. 1, 2011, the Church of Saints Mark and Peter in the northern city of Alexandria was bombed, killing 23 people as they left the New Year’s Day service. Ten months later, Egypt’s security forces killed 28 Christians protesting the demolition of a church, claiming the protesters first attacked them.

In 2013, Christians were targeted in a spate of attacks after Egypt’s elected Islamist president, Mohammed Morsi, was ousted in a military coup.

President Abdul Fattah al-Sisi, the former general who led the coup, declared three days of mourning.

“Vicious terrorism is being waged against the country’s Copts and Muslims,” he was quoted as saying on local television networks. “Egypt will emerge stronger and more united from this situation.”

The State Department declared: “The United States condemns in the strongest possible terms the terrorist attack today on Christian worshippers outside St. Mark’s Cathedral.”

Analysts focusing on Egypt’s religious divides said the government has made previous promises to apprehend the perpetrators of hate crimes. But it has shown few results.

“Sectarian tensions in Egypt is ongoing and this attack, although shocking in its scope, is not an aberration,” said Amira Mikhail, a fellow at the Tahir Institute for Middle East Policy.

Some reports on local television networks suggested that a bomb was placed inside a handbag in a section of the church designated for female worshippers. A large proportion of the victims were women.

Senior Egyptian officials, including the prime minister and interior minister, arrived at the church shortly after the attack. They were greeted by a small group of angry protesters who railed against the continuous attacks on Christians, as well as the security forces’ failure to stop the attacks.