Under pressure from Congress to speed access to U.S. skies for commercial drones, the government granted four companies permission Wednesday to use drones for aerial surveillance, construction site monitoring and oil rig flare stack inspections.

The new permits bring the total number of companies granted permits for commercial operations to 13. They were announced by the Federal Aviation Administration an hour before a House hearing at which lawmakers warned that if the agency doesn't move faster, Congress will step in.

Commercial drone flights are taking off in other countries while the U.S. lags behind in developing safety regulations that would permit unmanned aircraft operations by a wide array of industries, Gerald Dillingham of the Government Accountability Office testified at the hearing.

Several European countries have granted commercial permits to more than a 1,000 drone operators for safety inspections of infrastructure, such as railroad tracks, or to support commercial agriculture, Dillingham said. Australia has issued over 180 permits to businesses engaged in aerial surveying, photography and other work, but limits the permits to drones weighing less than 5 pounds. And small, unmanned helicopters have been used to monitor and spray crops in Japan for more than a decade.

Canada has had regulations governing the use of unmanned aircraft since 1996 and, as of September, had issued over 1,000 permits this year alone, Dillingham said.

The permits announced Wednesday were granted to Trimble Navigation Limited, VDOS Global LLC, Clayco Inc. and Woolpert Inc., which received two permits. The drones weigh less than 55 pounds and the firms have said they will they will keep the unmanned aircraft within line of sight of the operator.

Previously the only permits the Federal Aviation Administrational Aviation had issued were to two oil companies in Alaska and five aerial photography companies associated with television and film production.

The FAA said it has received 167 requests for exemptions from commercial entities.