Story highlights American and British spies have secretly monitored Israeli military drones, according to a report by The Intercept

The American and British spying are part of regular, ongoing international espionage

Washington (CNN) American and British spies have secretly monitored Israeli military drones, according to the latest investigative report by The Intercept.

Until now, Israel has kept its drone program secret -- refusing to even acknowledge that it uses them in warfare.

But now there's photo evidence from the drones themselves.

The images come from classified material in documents exposed by former U.S. National Security Agency contractor Edward Snowden.

CNN has reviewed the documents published by The Intercept, but the NSA, following agency policy, does not verify the authenticity of its exposed files.

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