(Reuters) - Four-time overall World Cup champion Lindsey Vonn has had surgery after breaking her right arm while training in Colorado and vowed to return to the slopes "as soon as possible".

The 32-year-old American said she "severely fractured" the humerus bone after an accident at Copper Mountain on Thursday and underwent surgery in Vail later that day.

"While I am beyond frustrated by this latest setback, at least my knees are ok and I will return to the slopes as soon as possible, as I always do!" Vonn posted on Facebook on Friday.

"Thank you for the continued love and support, it means so much to me."

It was the second time this year that the 2010 Olympic downhill champion had suffered a serious injury.

In late February while leading the World Cup standings, Vonn's Alpine ski season and title hopes were ended by a knee injury when she crashed after hitting a patch of soft snow in a super-G race in Andorra.

Further damage "could result in a serious surgery that would risk my future in ski racing", she said at the time.

Vonn, whose career has been punctuated by serious injuries, has won 76 World Cup races and is chasing Swedish great Ingemar Stenmark's record of 86.

(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Larry Fine)