Pontiff's final notes in Philadelphia

Thousands gathered as Pope Francis conducted a large open-air Mass in city's Benjamin Franklin Parkway, Philadelphia on Sunday, September 27, 2015, ending his six-day visit to the US.

Read: Pope Francis offers prayer to the Muslim community

He told the crowd to be open to "miracles of love for the sake of all the families of the world".

"The urgent challenge of protecting our home includes the effort to bring the entire human family together in the pursuit of a sustainable and integral development, for we know that things can change."

"I ask you to pray for me. Don't forget," he said.

Earlier, the pontiff prayed with a group of victims of child sexual abuse, saying "God weeps" for their suffering.

"Clergy and bishops abusing children would be held accountable," he said.

The Roman Catholic Church in the US has been embroiled in a series of child sex scandals, and US dioceses have made huge compensation pay-outs to victims in recent times.

Read: Pontiff meets victims of sexual abuse

The Pope approved the creation of a tribunal to hear cases of bishops accused of covering up child abuse by paedophile priests.

Read: Pope condemns 'boundless thirst' for wealth and power

However, many abuse survivors are angry at how the Vatican has dealt with allegations.