The Pontiff led thousands of people in prayer for the 29 victims, who he said were killed in “another act of ferocious violence” after having refused to renounce their Christian faith at gunpoint.

Speaking from his studio window over St Peter's Square, Francis said: “May the Lord welcome these courageous witnesses, these martyrs, in his peace and convert the hearts of the violent ones.”

Isis claimed responsibility for the attack on Christians travelling through the Minya region to the St Samuel the Confessor monastery.

Egypt shooting: Video shows destroyed bus in gun attack on Coptic Christians

The bus was blocked by three vehicles carrying eight to 10 attackers who opened fire, killing at least 29 and wounding 24, with many children among the victims.

Footage showed the bus raked with bullets, with its windows smashed, surrounded by dead bodies covered in black plastic sheets.

It was the fourth attack against Christians in Egypt claimed by Isis since December. The string of attacks have killed more than 100 and injured scores.

Video interviews with survivors painted a picture of untold horror as children hid under their seats to escape the gunfire.

In pictures: Coptic Christians mourn victims of Isis beheadings Show all 15 1 /15 In pictures: Coptic Christians mourn victims of Isis beheadings In pictures: Coptic Christians mourn victims of Isis beheadings Egypt Egyptian Coptics mourn for the 21 men murdered by Isis AP In pictures: Coptic Christians mourn victims of Isis beheadings Egypt A man is comforted by others as he mourns over Egyptian Coptic Christians who were captured in Libya and killed by militants affiliated with the Islamic State group, outside of the Virgin Mary church in the village of el-Aour, near Minya, 220 kilometers (135 miles) south of Cairo In pictures: Coptic Christians mourn victims of Isis beheadings Egypt Women mourn over Egyptian Coptic Christians who were captured in Libya and killed by Isis militants In pictures: Coptic Christians mourn victims of Isis beheadings Egypt A relative of one of the Egyptian Coptic Christians purportedly murdered by Isis reacts after hearing the news in the village of Al-Awar in Egypt's southern province of Minya In pictures: Coptic Christians mourn victims of Isis beheadings Egypt Relatives of Egyptian Coptic Christians purportedly murdered by Isis militants in Libya react after hearing the news in the village of al-Awar in Egypt's southern province of Minya In pictures: Coptic Christians mourn victims of Isis beheadings Egypt President Abdel Fattah al-Sisi offers his condolences to some of the Coptic families AFP In pictures: Coptic Christians mourn victims of Isis beheadings Egypt The Grand Imam of Al-Azhar, Sheikh Ahmed al-Tayeb (R) offers his condolences to Egypt's Coptic Pope Tawadros II at Saint-Mark's Coptic Cathedral in Cairo's al-Abbassiya district In pictures: Coptic Christians mourn victims of Isis beheadings Egypt A Coptic clergyman shows a picture of a man whom he says is one of the Egyptian Coptic Christians purportedly murdered by Isis militants in Libya, during a memorial ceremony in the village of al-Awar in Egypt's southern province of Minya In pictures: Coptic Christians mourn victims of Isis beheadings Egypt Relatives of Egyptian Coptic Christians murdered by Isis militants in Libya wlak through the village of Al-Awar in Egypt's southern province of Minya In pictures: Coptic Christians mourn victims of Isis beheadings Egypt A family relative of abducted Coptic Christian weeps AP In pictures: Coptic Christians mourn victims of Isis beheadings Egypt Men mourn over Egyptian Coptic Christians who were captured in Libya and killed by militants affiliated with the Islamic State group, inside of the Virgin Mary Church in the village of el-Aour, near Minya, 220 kilometers (135 miles) south of Cairo In pictures: Coptic Christians mourn victims of Isis beheadings Egypt Men mourn over Egyptian Coptic Christians who were captured in Libya and killed by militants affiliated with the Islamic State group, inside the Virgin Mary Church in the village of el-Aour, near Minya, 220 kilometers (135 miles) south of Cairo In pictures: Coptic Christians mourn victims of Isis beheadings Egypt Protesters hold placards during a demonstration against the killing of Egyptian Coptic Christians by militants of the Islamic State in Libya, in Cairo In pictures: Coptic Christians mourn victims of Isis beheadings Egypt Egyptians protest what they characterise as Government inaction in reaction to the kidnapping of Copts in Libya, Cairo EPA In pictures: Coptic Christians mourn victims of Isis beheadings Egypt A Coptic Christian woman prays for the release of 21 Coptic Egyptian men AP

One survivor, a small boy who seemed to be about six, said his mother pushed him under her seat and covered him with a bag.

A young woman speaking from her hospital bed said the assailants ordered the women to surrender their jewellery and money before they opened fire, killing the men first and then some of the women.

The woman said the gunmen were masked and wore military uniforms.

Dead bodies lay covered in black plastic sheets in the aftermath of the attack (AP)

Bishop Makarios, the top Coptic Orthodox cleric in Minya, the province where the attack took place, said the assailants told Christian men they ordered off the bus they would spare their lives if they converted to Islam.

“They chose death,” said Mr Makarios, who has been an outspoken critic of the government's handling of anti-Christian violence in Minya, where Christians account for more than 35 per cent of the population, the highest anywhere in Egypt.

“We take pride to die while holding on to our faith,” he said.

Mr Makarios confirmed the assailants stole the women's jewellery and his contention the men were ordered off the bus before being killed was also confirmed by a video clip purportedly taken in the immediate aftermath of the shooting.

The video showed at least four or five bodies of adult men lying on the desert sand next to the bus; women and other men screamed and cried as they stood or squatted next to the bodies.

Mourners react after the funeral of Coptic Christians who were killed on Friday in Minya, Egypt (Reuters) (REUTERS)

The Coptic church said it had received news of the killing of its “martyrs” with pain and sorrow.

Egypt responded to the attack with a wave of air strikes against suspected militant bases where the military said the perpetrators trained.

A manhunt for the assailants in the vast deserts to the west of the site of the attack has so far yielded no arrests.

On Saturday, the Pope said there are more Christian martyrs today than in ancient times.

Security guards stand near the site of an attack in Minya, Egypt, on 26 May (Reuters)

During a meeting with clergy in the Italian port city of Genoa, Francis urged them to pray “for our brothers the Egyptian Copts, who were killed because they did not want to renounce their faith”.

“Let’s not forget that today there are more Christian martyrs than in ancient times, than in the early day times of the church,” he told bishops, priests and nuns gathered in the Cathedral of San Lorenzo.

He has previously paid tribute to Christians in the Middle East who have been persecuted by Islamist militants and he has often denounced Isis and condemned the concept of killing in God's name.

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The attack is the second time Isis has targeted the beleaguered Christian minority in Egypt in recent months following twin bombings that killed at least 44 people in churches in Tanta and Alexandria on Palm Sunday last month.

Isis has targeted numerous religious minorities including Coptic Christians – who have been beheaded in Libya – and Sufi and Shia Muslims, who have been massacred across the Middle East.

It has also particularly persecuted the Yazidi communities in Iraq – men were murdered and women were sold into sex slavery when the group declared its “caliphate” in 2014.