It was a rare day at the Vatican on Wednesday as two popes shared the limelight in St Peter's Square - Pope Francis and His Holiness Pope Tawadros II of the Coptic Orthodox Church.

Tawadros, dressed in black robes, was the guest of honour at Francis' general audience in a rainy St. Peter's Square. The two sat near each other and delivered a joint blessing at the end.

Tawadros, 70, is at the Vatican to mark the 50th anniversary of the first meeting between a Roman pope and a Coptic pope which took place between their respective predecessors, Shenouda III and Paul VI, in 1973.

In his greeting to Tawadros, Francis recalled the 20 Egyptian Copts who were kidnapped and beheaded on a beach in Libya by Islamic State in 2015.

"Martyrs of the Coptic Church are ours too," Francis, 86,  said.

The 20 Copts and one Ghanaian Christian were lined up on a Libyan beach in orange jumpsuits before they were executed in the Libyan city of Sirte, which Islamic State controlled between 2015-2017. The Islamist group posted a video of the killings, showing the men praying to Jesus as they died.

The victims, whose bodies were returned to Egypt in 2018, were among the many poor Egyptians who risked their lives to find work in the lawless chaos of Libya following the downfall of Muammar Gaddafi in 2011 and civil war.

Copts comprise about 10 percent of Egypt's mostly Muslim population and there are small Coptic Christian communities throughout the Middle East and Africa. They have long been attacked by Islamist militants who see them as heretics.

Coptic Orthodox Christians trace their origins to St. Mark the Apostle.

Tawadros is due to have a private meeting with Francis on Thursday and visit the Vatican department that promotes Christian unity.