Vatican City ? An increasingly frail Pope John Paul II missed his general audience Wednesday — a rare absence — because of a mild intestinal problem, raising fresh concerns about his health just weeks before he presides at ceremonies marking his 25th anniversary as pope.

The 83-year-old pontiff managed to address the crowd at the Vatican in an audio message, although he spoke with a weak voice and slurred his words — symptoms of the Parkinson’s disease he has had for years.

“I am sorry for not being with you,” John Paul said. “I carry you all in my heart and I bless you with affection.”

The pontiff was to have traveled from his vacation home in Castel Gandolfo, south of Rome, to Vatican City to greet thousands of the faithful and tourists. But his doctors advised against the trip after he came down with a mild “intestinal indisposition” Tuesday afternoon, the Vatican said.

Papal spokesman Joaquin Navarro-Valls said John Paul would keep to his upcoming schedule. That includes moving Friday back to the Vatican and meeting with Philippines President Gloria Macapagal Arroyo on Saturday.

The illness comes at a busy time for the John Paul. On Oct. 4, he is due to meet the Archbishop of Canterbury, Rowan Williams, for talks at the Vatican that are likely to touch on the explosive decision of the U.S. Episcopal Church to elect its first openly gay bishop.

On Oct. 16, John Paul celebrates his 25th anniversary as pope with an evening Mass in St. Peter’s Square. He is due to make public appearances before and after that, including a speech to the College of Cardinals, all of whom have been invited to Rome for the anniversary celebrations.

On Oct. 19, John Paul is due to beatify Mother Teresa.