The relatives of British aid workers murdered by Islamic State met with Pope Francis at the Vatican on Wednesday.

Michael Haines, the brother of David Haines, and Barbara Henning, Alan Henning's widow, spoke to the Pope at the end of the general audience on the steps of St Peter's Basilica.

Haines and Henning were both beheaded by ISIS militants last year, with videos of their murders released online. Haines was abducted in March 2013 while working in Syrian refugee camps. Henning was part of a group of volunteers that travelled to Syria in December 2013 to help bring food and water to those affected by the civil war. He was captured by masked gunmen just after Christmas.

Mike Haines, who has been working to promote inter-faith unity since his brother's death, said meeting the pope "took my breath away".

Francis promised to pray for him, and to "continue the work we're doing on unity and tolerance and bringing our communities together," he added.

Barbara Henning received a blessing from the pope during her visit.

The two appealed to churches, synagogues and mosques to open their doors to people of all faiths in a letter last October, following the murder of their relatives.

They said they wrote it because they did not want "the actions of a few people to undermine the unity of people of all faiths in our society.

"David and Alan were never more alive than when helping to alleviate the suffering of others. They gave their lives to this cause and we are incredibly proud of them," the letter read.

"Together we have the power to defeat the most hateful acts. Acts of unity from us all will in turn make us stronger and those who wish to divide us weaker...We urge churches, mosques and synagogues to open their doors and welcome people of all faiths and none. All these simple acts of unity will, in their thousands, come together to unite us and celebrate the lives of David and Alan."

Pope Francis has repeatedly condemned the violence perpetrated by ISIS militants. In November last year he branded it a "profoundly grave sin against God".

"Taking away the peace of a people, committing every act of violence, especially when directed against the weakest and defenseless, is a profoundly grave sin against God, since it means showing contempt for the image of God which is in man," he said.