Pope Benedict XVI began a controversial four-day state visit to the United Kingdom on Thursday.
Many are protesting the pope's visit, angry at sex abuse scandals that have rocked the Catholic Church. Benedict acknowledged that sentiment and told reporters the church did not act quickly or forcefully enough against priests who sexually abused children.
Benedict also said abusive priests must never have access to children, saying they suffered from an illness that mere "goodwill" couldn't cure.
He said he felt "sadness also that the church authority was not sufficiently vigilant and not sufficiently quick and decisive to take the necessary measures" to stop the abuse and prevent it from occurring again. The pope said the victims were the church's top priority now.
The pope's first meeting Thursday was with Queen Elizabeth II, both head of state and head of the Church of England, at a palace in Scotland. Prince Philip, the husband of Queen Elizabeth, met the pontiff at Edinburgh airport.
This is the first time a pope has made a state visit to the United Kingdom, an officially Protestant nation.
The queen is head of the Church of England, which split acrimoniously from Rome in the 16th century - a division followed by centuries of anti-Catholic sentiment. The visit also coincides with the 450th anniversary of the Reformation in Scotland.
Benedict acknowledged the opposition, saying Britain had a "great history of anti-Catholicism. But it is also a country with a great history of tolerance."
The last papal visit to Britain was by John Paul II in 1982. Benedict's trip to Britain is a state visit because he was invited by the monarch.