Pope Francis takes Syrian refugees on aircraft from Greece

Three families of Syrian refugees boarded Pope Francis's plane heading back to the Vatican on April 16 after his lightning visit to a Greek island on the frontline of Europe's migrant crisis, a Reuters witness said.

"The Pope has desired to make a gesture of welcome regarding refugees, accompanying on his plane to Rome three families of refugees from Syria, 12 people in all, including six children," a statement issued by the Vatican said.

Pope Francis arrived on the Greek island of Lesbos on April 16, turning the world's attention to the frontline of Europe's migrant crisis which has claimed hundreds of lives in the past year.

Greek Prime Minister Alexis Tsipras, Fener Rum Patriarch Dimitri Bartholomeos and Archbishop of Athens welcomed him at the airport.

Francis, leader of the world's 1.2 billion Roman Catholics, was scheduled to spend about six hours on the small Aegean island. Based on his schedule, he was to meet 250 refugees and have lunch with eight of them.

Hundreds of people have died making the short but precarious crossing from Turkey to the Lesbos shores in inflatable dinghies in the past year, and the island is full of unmarked graves.

"This is a trip that is a bit different than the others ... this is a trip marked by sadness," Francis told reporters on the airplane taking him to Lesbos.

"We are going to encounter the greatest humanitarian catastrophe since World War Two. We will see many people who are suffering, who don't know where to go, who had to flee.

We are also going to a cemetery, the sea. So many people died there ... this is what is in my heart as I make this trip."

Francis will visit Moria, a sprawling, fenced complex holding more than 3,000 refugees.

"This is an island which has...