Actors Brad Pitt and Angelina Jolie arrive for the New York Film Festival premiere of "Changeling" in New York October 4.- Xinhua/Agencies

Brad Pitt has reportedly turned down a marriage proposal from Angelina Jolie. Angelina - who raises six children with the actor - is said to be desperate to wed, but Brad wants to attend couples counselling before they tie the knot.

A source told National Enquirer magazine: "Angelina proposed to Brad recently and suggested a Christmas wedding. When Brad insisted they hold off, Angelina put him on a major guilt trip by telling him the kids want them to be married."

Brad thinks a wedding right now is biting off more than they can chew. He would like to slow down and go through some couples counselling. But Angelina is insisting they get married before they adopt again or have another biological baby." It has also been claimed 33-year-old Angelina is undergoing fertility treatments in a bid to conceive a second set of biological twins with Brad, 45.

A source said: "Angelina's doctors told her she has a strong chance of conceiving twins if she does it within two years after having her first pair. She has been seeing a fertility doctor regularly. She and Brad are monitoring when she is fertile. And they are trying really hard in the bedroom!"