Migrants rescued from two boats in the Mediterranean this week told humanitarian workers in Italy that they saw another vessel carrying some 400 migrants sink, Save the Children said on Saturday.

Three vessels carrying migrants already are confirmed to have sunk or capsized this week. More than 60 bodies are said to have been recovered, including those of three infants, and hundreds are believed to be missing.

But the possible sinking of a fourth vessel on Thursday had not been reported, said Giovanna Di Benedetto, spokeswoman for Save the Children in Italy.

That ship along with another fishing boat and a rubber boat left Sabratha in Libya late Wednesday night, according to interviews on Saturday with some of the more than 600 survivors from the two other vessels in the Sicilian port of Pozzallo.

They said the rubber boat had its own motor, but the smaller fishing boat, carrying some 400 migrants, did not. It was towed by the larger fishing vessel, which held about 500 others.

Eventually the smaller boat began to take on water and, when the captain of the larger boat ordered the tow line cut, sank with most of its passengers, the survivors told Save the Children. Those aboard the other two vessels were not rescued until much later.

"There were many women and children on board," the survivors said, according to Di Benedetto. "We collected testimony from several of those rescued from both (the rubber and fishing) boats. They all say they saw the same thing."

On the orders of the court of Ragusa, police have detained a man who they suspect was the captain of the larger boat, state news agency Ansa reported. Police are interviewing witnesses of the possible tragedy, la Repubblica Web site said.

Mild weather has brought on a surge in migrant traffic this week between Libya and Italy, and about 700 more migrants were picked up on Saturday, the coast guard said.

Pope Francis met with children at the Vatican earlier in the day to talk about migration, urging them to welcome migrants because they "are not dangerous, but in danger." – Reuters