Online giant Amazon has sought permission for drone test flights in the United States, saying it is moving forward on plans for deliveries using the unmanned aircraft.

In a letter to the Federal Aviation Administration made public this week, Amazon said that because of restrictions on drones in US airspace, it has been conducting test flights indoors and in other countries.

"Of course, Amazon would prefer to keep the focus, jobs, and investment of this important research and development initiative in the United States by conducting private research and development operations outdoors near Seattle," the letter said.

Amazon said an exemption to FAA rules would be "in the public interest" and "is a necessary step towards realizing the consumer benefits of Amazon Prime Air," which company founder Jeff Bezos has described as a plan for drone delivery to consumers.

Bezos unveiled his idea for drone deliveries last December, and said the company would be ready to launch Amazon Prime Air as early as 2015 if FAA regulations allowed.

The letter said that over the past five months, "we have made advancements toward the development of highly-automated aerial vehicles for Prime Air," which travel at over 50 miles (80 kilometers) per hour and can carry loads up to five pounds (2.2 kilos).

The letter to the FAA said the granting the request "will do nothing more than allow Amazon to do what thousands of hobbyists and manufacturers of model aircraft do every day, and we will abide by much stronger safety measures than currently required for these groups."

Amazon's plan is to allow for deliveries of some goods within 30 minutes of an order.

Amazon said it would conduct the tests on its own property in the northwest state of Washington, and on FAA-approved test sites.

It added that "one day, seeing Amazon Prime Air will be as normal as seeing mail trucks on the road today, resulting in enormous benefits for consumers across the nation."

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