An American climber has been killed on Nepal's Mount Everest after he slipped and fell into a crevasse.

Delayed reports from the region say 39-year-old Michael O'Brien fell to his death Sunday as he and his brother, Chris, were attempting to become the first American brothers to climb the mountain together.

The two started their climb last month to raise money for the Hereditary Disease Foundation, which funds research to find cures for diseases like Alzheimer's and Parkinson's. Michael O'Brien is the second casualty on Mount Everest this year.

A Canadian climber was killed there last week. Since Mount Everest was first conquered in 1953, more than 1,400 people have scaled the 8,900-meter mountain and about 180 people have died on its slopes.

Some information for this report provided by AP and Reuters.