BELLVUE United States — Amazon.com Inc has won approval from U.S. federal regulators to test a delivery drone outdoors, less than a month after the e-commerce powerhouse blasted regulators for being slow to approve commercial drone testing.

The Federal Aviation Administration had earlier given the green light to an Amazon prototype drone in March, but the company told U.S. lawmakers less than a week later that the prototype had already become obsolete while it waited more than six months for the agency's permission.

The FAA granted Amazon's request to test delivery drones in a letter dated Wednesday, posted on the agency's website.

Amazon must keep flights at an altitude of no more than 400 feet (120 meters) and no faster than 100 miles per hour (160 km per hour), according to the letter.

Seattle-based Amazon.com has been pursuing its goal of sending packages to customers by air, using small, self-piloted aircraft, even as it faces public concern about safety and privacy.

The company wants to use drones to deliver packages to its customers over distances of 10 miles (16 km) or more, which would require drones to travel autonomously while equipped with technology to avoid collisions with other aircraft.

In February, the FAA proposed long-awaited rules to try to set U.S. guidelines for drones, addressing growing interest from both individual and corporations in using unmanned aerial vehicles.

Amazon did not immediately respond to requests for comment.

By Sai Sachin R; editor: Lisa Shumaker.