The 11 colour screen-prints, thought to be worth several million pounds, were taken from businessman Richard Weisman's home between September 2 and 3.

Ten of the portraits, each 40 inches by 40 inches, feature famous athletes of the 1970s, including golfer Jack Nicklaus, soccer star Pele and figure skater Dorothy Hamill. The other is of Mr Weisman.

A $1 million (£600,000) reward is being offered for information leading to the return of the artwork.

The original prints were on display in Mr Weisman's dining room and his house was locked. It was not clear exactly when the silk screen paintings were taken or how the thieves got into the home.

There was no sign of forced entry and several other valuable paintings were left untouched.

The theft was discovered by the family nanny who arrived at the home to find the prints missing from the walls. She immediately went to a neighbour's to call police, said Detective Mark Sommer of the Los Angeles Police Department's art theft unit.

"This was a very clean crime," he said. "(The home) wasn't ransacked."

Mr Weisman, who published a book about his art collection called From Picasso to Pop, tried to sell the collection in 2002 for $3 million (£1.8 million)...