Warhol: Images defined a generation

Both lots exceeded their pre-sale estimates and contributed to a total fund of almost $730,000 (�507,000) for 23 lots of Warhol's work.

The Monroe portfolio consisted of 10 vibrant, fluorescent colour prints, which are considered to be some of the most iconic images of the Pop Art era.

The portfolio, sold by a California collector, was one of Warhol's 26 copies from a total of 250 published by Factory Additions, New York, in 1967.

It exceeded its $275,000-300,000 pre-sale estimate to make it the most expensive lot of the two-day auction.

Warhol, who died in 1987 aged 57, is well known for his images which blend the iconography of advertising with traditional painting techniques.

The Mao prints are some of Warhol's best-known

Sotheby's Modern Art specialist Mary Bartow said before the sale that it was rare to find a set of Monroe prints still kept together.

She said "These pictures have never been framed and are in very good condition, the colours are very fresh.

"The owner has never even taken them out of the box they came in."

She added: "To find a complete set of Marilyn silk screens is rare, and it's a wonderful depiction of 20th Century art."

Warhol's orange Marilyn screen print sold for �10.6m ($15.2m) when in 1998 - more than five times the pre-sale estimate.

The 10 Mao prints came from the cover of Quotations from Chairman Mao Tse-Tung, published in 1972, the same year that President Richard Nixon travelled to China.