Two U.S. jet fighter pilots died Saturday when their F-15E crashed in eastern Afghanistan, officials said.

Their deaths brought the American death toll in Afghanistan to 26 for July, and 50 for the NATO-led coalition, making it the deadliest month yet for Western forces in the 8-year-old Afghan conflict, the Los Angeles Times reported.

The upsurge in deaths among U.S., British and Canadian troops are a result of a build-up of troops and a push into insurgent-controlled areas of the country, military officials say, warning of more casualties in the coming months.

Military officials told the Times they were conducting an investigation of the jet crash, but have ruled out the possibility it was shot down by enemy fire.

"The crash was not due to hostile fire," U.S. forces in Afghanistan said in a statement.