Palestinian president Mahmoud Abbas has been invited to the Vatican for the canonisation mass of two Palestinian nuns.

He was invited by Patriarch Fouad Twal of Jerusalem during a visit to Abbas' headquarters in Ramallah. The visit on May 17 will be Abbas' second, after a meeting there with the Pope and Israeli president Shimon Peres last June.

The two nuns, Blessed Marie-Alphonsine Ghattas and Blessed Mariam Baouardy, both founded religious orders.

Blessed Marie-Alphonsine (1843-1927) was the co-foundress of the Congregation of the Rosary Sisters. She spent much of her life in Bethlehem and the surrounding area, assisting the poor and establishing schools and orphanages.

Blessed Mary of Jesus Crucified (Mariam Baouardy, 1846-78) was a Turkish Palestinian who founded the Discalced Carmelites of Bethlehem. Her family were of the Melkite-Greek Catholic Church and she spent time in France and India.

In a pastoral letter, Patriarch Twal called the two women "a blessing from heaven on our land, devastated by violence yet persevering in our longing for peace and justice".

"This long-awaited announcement of the double canonization restores in us our trust and hope in Christ," he wrote. The Lord wants to comfort our country, torn apart by conflicts and wars, and our people, who continue to suffer and endure through injustices."

He said that "the tribulations which we endure encourage us to become saints, through the example of our two holy women. This is not something impossible to do."