VATICAN CITY (CNS) — Marking 40 years of ecumenical dialogue, Pope Francis told the leader of 10 million Coptic Orthodox that their churches are united by an “ecumenism of suffering.”

“Just as the blood of the martyrs was a seed of strength and fertility for the church, so too the sharing of daily sufferings can become an effective instrument of unity,” Pope Francis told Pope Tawadros II May 10.

The remark appeared to refer to increased violence over recent decades against Coptic Christians in Egypt, including a car bomb that exploded outside a church in Alexandria on New Year’s Eve 2011, killing at least 21 people.

The principle of unity through suffering “also applies, in a certain sense, to the broader context of society and relations between Christians and non-Christians,” Pope Francis said. “From shared suffering can blossom forth forgiveness, reconciliation and peace, with God’s help.”

Orthodox make up about 9 percent of Egypt’s population of 85 million, which is 90 percent Muslim. Catholics in Egypt, who are in full communion with Rome, number about 165,000.

In his remarks, Pope Tawadros said that his church “has been irrigated until now with the blood of numerous martyrs, thus becoming stronger and stronger,” but made no reference to specific events.

The meeting between the two popes came on the 40th anniversary of one between Pope Paul VI and Pope Shenouda III, who signed a declaration of their churches’ common understanding of Christ and established a formal ecumenical dialogue.

Recalling that event, Pope Tawadros told Pope Francis that May 10 “should be considered as a celebration of brotherly love between the Catholic Church and the Coptic Orthodox Church.”

The Orthodox leader also invited Pope Francis to visit Egypt and later told Vatican Radio that the pope had accepted his invitation.

Following their meeting in the papal library, the two popes moved to the Apostolic Palace’s Redemptoris Mater Chapel, where they led a prayer service that included Coptic chant and the Our Father recited in Italian.