At a ceremony in Atlanta organised by the Online News Association, the Guardian was awarded the Gannett Foundation Award for Investigative Journalism and the Watchdog Journalism Award.
Guardian US editor in chief Janine Gibson, said: "We're very proud to accept these awards from the ONA and the Gannett Foundation. It means a great deal to have the endorsement of our peers in the US media and we are thankful for their support.
"These awards are significant, not just to our team who have worked relentlessly for months on this story, but because they recognise the importance of difficult watchdog journalism in the public interest."
The Online News Association was founded in 1999 and has more than 2,000 members around the world.
