Amazon.com Inc.'s drone delivery test program is back in business in the U.S. after it received a new approval from regulators.

The Federal Aviation Administration gave the online retailer a waiver allowing flights as fast as 100 miles (161 kilometers) an hour and as high as 400 feet off the ground, according to a letter dated Wednesday posted on its website.

An earlier FAA approval under a separate program hadn't been of use to the company because it applied to a specific drone model no longer in use, Paul Misener, an Amazon vice president, told Congress on March 24.

Amazon is attempting to develop autonomous drones that can dodge obstacles and find specific addresses to speed the delivery of small packages. The company has been frustrated with the pace of FAA approvals and has been forced to conduct some tests in other countries, Misener said.

The FAA on Feb. 15 unveiled its first set of proposed rules for commercial drone flights. Those initial rules wouldn't permit such automated activity because they require operators to keep their drones within sight at all times.