Pope Francis has spoken of a Syrian Christian "martyr" in a speech in St Peter's Square, after arriving in Rome with 12 refugees from the island of Lesbos. The six children and their parents were taken to Italy after the Pope visited the refugee camps in Greece.

All 12 of the refugees are Syrian Muslims. "All refugees are children of God," the Pope said on his flight back to Rome. He also said that the gesture was "a drop in the ocean" but that he hoped "the ocean will never be the same again".

Talking to Italian newspaper La Stampa, the families called Pope Francis their "savior" and hailed his "gesture of hope".

Speaking to the audience gathered in St Peter's Square, the Pontiff said that he had met 300 refugees in Lesbos on Saturday, including a man whose wife had been killed by extremists for refusing to renounce her Christian faith.

"He is Muslim, and he told me that he married a Christian girl. They loved each other and respected each other…'But unfortunately, the young woman's throat was slashed by terrorists because she didn't want to deny Christ and abandon her faith," the Pope said, also saying: "She is a martyr."

The Vatican has said that it will be responsible for looking after the 12 refugees, with help from the Community of Sant'Egidio – the Catholic Church's association of lay members. According to UN figures, Vatican City had a population of 451 in 2012 – with yesterday's arrival of the 12 refugees, there are now 20 refugees there.

Pope Francis was greeted by Greek prime minister Alex Tspiras on his arrival in Lesbos and was joined in the camp by Patriarch Bartholomew, the Archbishop of Constantinople and leader of the world's 300 million Orthodox Christians, and Archbishop Ieronymos II, leader of the Greek Orthodox Church.