The Oscar-winning beauty - who already has an 18-month-old biological daughter Shiloh, as well as three adopted children, Maddox, six, Pax, three, and two-year-old Zahara, with partner Brad Pitt - canceled a lecture she was due to give at the UN-linked Pio Manzu center, near Rimini, Italy, due to "personal reasons."

Italian newspapers claim the actress - who is a UN ambassador - had to pull out at the last minute because she had discovered she was expecting.

Letizia Manjani, a spokeswoman for the center, refused to rule out a pregnancy.

She said: "Angelina canceled last week. Due to her privacy I can't confirm her pregnancy, but I can say that the Italian newspapers are correct in their reports."

Angelina and Brad - who first met on the set of "Mr. and Mrs. Smith" - have made no secret of their desire to add to their family.

Brad recently revealed they were keen to welcome a fifth child into their family, saying: "We're ready."

The "Fight Club" star said fatherhood is "the most fun" he's ever had, although he is constantly sleep deprived.

He said: "It's the most fun I've ever had and also the biggest pain... I've ever experienced. I love it and can't recommend it any more highly - although sleep is non-existent!"