The centuries-old divide between the Church of England and the Roman Catholic Church is a "scandal", Pope Francis said as he met the Archbishop of Canterbury in Rome.
The leader of 1.2 billion Catholics worldwide said a goal of full unity between the two churches "may seem distant" but it remained an aim that should direct "every step".
He said progress towards full unity would not be the result of human actions alone, but would be a "free gift of God".
"Beneath his merciful gaze, we cannot claim that our division is anything less than a scandal and an obstacle to our proclaiming the Gospel of salvation to the world," the Pope told Archbishop Justin Welby.
"Our vision is often blurred by the cumulative burden of our divisions and our will is not always free of that human ambition which can accompany even our desire to preach the Gospel as the Lord commanded."
The Pope was speaking as the two men met at the Vatican for the second time since they were installed as leaders of their churches last year.
The Archbishop's visit to Rome, which began on Saturday, focused on work by the churches to eliminate human trafficking and modern-day slavery.
Mr Welby described human trafficking and slavery as "a grave crime" against humanity.
He also praised the Pope's "remarkable" care for the poor and suffering, and his "passion" for reconciliation, witnessed recently in his visit to the Middle East.
He said he hoped that the collaboration with Pope Francis would lead to an "effective challenge" to the "unspeakable disasters of war and conflict" throughout the world.
Mr Welby - who gave a gift to the Pope of a cutting from a fig tree in Lambeth Palace planted by the last Roman Catholic archbishop of Canterbury, Cardinal Pole - added that the Church of England remained "deeply committed" to ecumenical talks.
But he added: "I realise that there are matters of deep significance that separate us."
The meeting comes as the General Synod is widely expected to give final approval next month to legislation introducing the first woman bishops in the Church of England, making the prospect of unity between the two churches appear more distant.
The Roman Catholic Church does not allow women to become priests.