Roberts won the best actress Oscar in 2001 for Erin Brockovich

The 36-year-old star, who won the best actress Oscar for Erin Brockovich, is due to give birth early next year, her spokeswoman told BBC News Online.

They will be the first children for Roberts, who married cinematographer Daniel Moder, 35, two years ago at her home in New Mexico.

Twins run in Roberts' family, with her great grandmother and a pair of cousins born as twins, her spokeswoman said.

'Will of heaven'

The announcement followed rumours that Roberts was pregnant two years ago, which turned out to be false.

"I think children fall into the category of the will of heaven, and I don't really have a timetable for that," Roberts said in 2002.

The latest speculation began after the actress was photographed on a beach in Italy, apparently with a bump.

In addition to her Oscar win, Roberts was nominated for the best actress Oscar for 1990's Pretty Woman and a best supporting actress Oscar for 1989's Steel Magnolias.

She recently starred in Mona Lisa Smile and is current filming Ocean's Twelve, the sequel to 2001 hit movie Ocean's Eleven, in Italy.