The comments came after Amazon told a US Senate committee that the country's reticence was holding it back.
The firm said that, by the time it had been given permission to test one prototype, the drone had already been rendered obsolete.
The US Federal Aviation Administration (FAA) said the congestion of America's airspace justified its slow approach.
Paul Misener, Amazon's vice president for global public policy, told the committee earlier this week that permission to conduct outdoor tests on a home delivery drone prototype had taken more than six months to be granted, and came through about a week ago.
"We don't test it anymore. We've moved on to more advanced designs that we are already testing abroad," he said.
Mr Misener told the Senate Subcommittee on Aviation Operations, Safety and Security: "Nowhere outside of the United States have we been required to wait more than one or two months to begin testing."
Amazon has previously said it wanted to use drones to deliver packages to people's homes. The flights would cover distances of 10 miles (16 km) or more and would require drones to travel autonomously while equipped with technology to avoid collisions with other aircraft.
The case illustrates the frustrations of many industry representatives, who have said that the US regulatory process is not keeping up with rapidly developing drone technology that could generate new revenues and cost savings for a range of industries.
The FAA has sought to alleviate some of the frustrations by announcing a new "blanket" approval for some companies to fly limited operations, rather than requiring a new permit for each flight.
The change affected only flights of up to 200ft (61m) during daylight hours and within a drone operator's line of sight.
But concerns over the restrictive US policies could provide an opportunity for the UK, according to Dr Ravi Vaidyanathan, a senior lecturer in robotics at Imperial College London.
"For commercial growth, it probably does provide an opportunity because companies can do more [in the UK], so they can gauge more of the market and the likely impact," he told the BBC.
A House of Lords committee has called for strict controls to be placed on the use of drones, but also for the flexibility to allow the growth of a burgeoning industry that experts have said could create thousands of jobs.
Mr Misener called the approach of the European authorities more "reasonable", adding that the US government's "low level of... attention and slow pace" was inadequate.
However, Dr Vaidyanathan highlighted the "potential downside" in reducing regulatory requirements, saying that doing so would create a greater safety risk.
And Margaret Gilligan, the FAA's associate administrator for aviation safety, said that US airspace was more complex than that of other countries. She told the Senate panel that regulators could set new standards for autonomous drone operations within a year.
The FAA recently proposed rules that would lift the current ban on most commercial drone flights, but several restrictions attached would make package delivery and other business applications unfeasible.
Among other constraints, the proposed rules would limit commercial drones to an altitude of 500ft (150m), as well as allowing flights only during daytime and requiring operators to keep the aircraft in sight at all times.
The agency does not expect to finalise the rules until late 2016 or early 2017, according to government officials. During this period, the current ban will stay in place. Companies can apply for exemptions to use drones for specific business applications.
US regulators' sluggishness over drone testing could be an opportunity for the UK, a leading academic has said.