A media representative for Egypt's Catholic bishops echoed concerns that police sided with Islamic extremists who attacked a funeral service en masse at St. Mark's Coptic Orthodox Cathedral in Cairo.

"The police must have been aware of the situation. So why were the police not in front of the cathedral?" asked Father Rafik Greiche of the Egyptian Catholic bishops' conference.

He told Catholic charity Aid to the Church in Need that the police "only arrived two hours later, and then they protected the attackers." Muslim extremists had previously threatened to disrupt the service, the priest said.

The April 7 funeral was for four Christians killed in a gunfight that followed a dispute in the town of Khusus near Cairo. A Muslim was also killed in that clash.

After the Christians' funeral, mourners left the cathedral and joined sympathetic Muslims in chanting slogans against President Mohammed Morsi and calling for his removal.

At some point violence broke out for unclear reasons. At its worst, 200 people attacked the Christians, some throwing stones and petrol bombs from the roofs of buildings surrounding the cathedral.

Christians took up the defense of the cathedral and threw fire bombs and brick shards at the riot police, some of whom were injured.

The clash lasted until late in the evening. Two were killed and more than 90 hurt. The New York Times is among the media outlets reporting the apparent alliance between the attackers and the riot police.

Coptic Catholic Bishop Kyrillos William Samaan of Assiut has condemned the attack.

"Nobody could have imagined that anybody would attack such an important symbol for all Egyptians as St Mark's Cathedral in Cairo," the bishop said. "It is shocking. But we will never learn the real motives for these attacks."

Fr. Greiche said that other local Muslims have voiced their support and sympathy for the Christian community.

"All of our Muslim friends told us that the events make them feel ashamed," he said.

The priest recently visited Azhar University, a prominent Sunni institution, noting that the sheiks there "assured us that such attacks are not compatible with Islam."

The attack also drew condemnation from Egyptian President Mohammed Morsi, who said he regarded any attack on churches as "a personal attack" against him.

Despite the president's words, some Egyptian Christians told Reuters news service that the violence has prompted them to consider leaving their homeland.

Orthodox Coptic leader Pope Tawadros II said the president has not done everything he could to protect the cathedral.

"We want actions, not words," he said.

Fr. Greiche said the violence comes at a time of improving relations between Egyptian Catholics and other Christians. The Catholic leadership is in "permanent contact" with the Protestant and Orthodox Churches in Egypt.

He said relations with the Coptic Orthodox have "completely transformed" since the election of Pope Tawadros in November 2012.

"Tawadros is very open," he added. The Orthodox Pope attended the enthronement of the new Coptic Catholic Patriarch Ibrahim Isaac.

"That had never happened before," he said.

Another unprecedented event in Egyptian Christian relations is still in development. Pope Tawadros intends to visit Pope Francis in Rome.