Image caption Brad Pitt and Angelina Jolie have championed humanitarian causes and set up charitable organisations

Hollywood A-listers Angelina Jolie, 36, and Brad Pitt, 48, are engaged to be married, a spokeswoman has confirmed.

But no wedding date has yet been set, she added, describing the engagement as "a promise for the future".

The couple, who are among Hollywood's most widely recognised celebrities, have been together since 2005.

They have six children together, including three adopted children. They are "very happy" about the news, the spokeswoman said.

Jolie, the daughter of actor Jon Voight and actress Marcheline Bertrand, has starred in blockbuster films such as Mr & Mrs Smith, where she met Pitt. She won an Oscar for her performance in the 1999 film Girl, Interrupted.

She was previously married to actors Jonny Lee Miller and Billy Bob Thornton.

Meanwhile, Pitt has starred in a string of hit films including blockbusters Ocean's Eleven, Seven and, more recently, the critically acclaimed Moneyball and Tree of Life.

Earlier, Pitt had high-profile relationships with actresses Gwyneth Paltrow and Jennifer Aniston, to whom he was married.

As a couple Pitt and Jolie have championed humanitarian causes.

In 2001 she became a goodwill ambassador for the United Nations High Commissioner for Refugees (UNHCR). She has also established a number of charitable organisations, among them the Jolie-Pitt Foundation.