The National Park Service took steps on Friday to ban the use of unmanned aircraft, or drones, in America's national parks, citing visitor complaints and concerns over wildlife harassment.

The agency's director, Jonathan B. Jarvis, signed a policy memorandum directing park superintendents to prohibit the launching, landing or operation of unmanned aircraft in their parks.

"We embrace many activities in national parks because they enhance visitor experiences with the iconic natural, historic and cultural landscapes in our care," Jarvis said in a statement. "However, we have serious concerns about the negative impact that flying unmanned aircraft is having in parks."

The parks are banning the use of unmanned aircraft "until we can determine the most appropriate policy that will protect park resources and provide all visitors with a rich experience," Jarvis said.

Officials said the policy is a temporary measure until the Park Service can hammer out a nationwide resolution on unmanned aircraft. That process can be lengthy, designed to include public notice of the proposed regulation and an opportunity for public comment.

Some individual parks have already outlawed drones, including Grand Canyon National Park in Arizona and Zion National Park in Utah.

At the Grand Canyon in April, visitors were gathered to watch the sunset when a loud unmanned aircraft interrupted, flying back and forth before eventually crashing beyond the rim of the canyon, officials said. Later that month, volunteers at Zion National Park reported watching an unmanned aircraft disturb a herd of bighorn sheep.

Last September, an unmanned aircraft flew over visitors seated in the Mount Rushmore National Memorial Amphitheater. It was later confiscated by park rangers.

No specific drone-related incidents have surfaced in Alaska's national parks, said Morgan Warthin, a regional National Park Service spokeswoman. But she said evidence of the use of unmanned aircraft in Alaska's parks has surfaced in online videos.

One YouTube video posted on Sunday, for example, shows footage of Denali National Park captured by an unmanned aircraft called the DJI Phantom 2.

Warthin said other posted videos suggest filming has also taken place in the Katmai and Kenai Fjords national parks.

"Absolutely, we are concerned," Warthin said.

Jeffrey Olson, a spokesman for the Park Service in Washington D.C., said unmanned aircraft appear to be generally popular for capturing video footage, or even still photography.

The no-drone policy will be enforced by park rangers, Olson said in a follow-up email, adding that rangers can act on a case-by-case basis "and will do so with a light hand."

"It may be as simple as reminding someone of the rule and asking them to put the unmanned aircraft back in their vehicle," Olson said. If a ranger has to write up a citation, he said, it will be a misdemeanor offense.

Olson said the Park Service consulted with the Federal Aviation Administration on the policy, but the action is separate from the FAA's ban on commercial drone flights.

In the parks, all previous permits issued for unmanned aircraft are being suspended until they have been reviewed and approved by park officials. If a superintendent earlier issued a permit allowing the use of model aircraft for hobbyist or recreational use, those uses can continue, the Park Service said.

The Park Service said it may use unmanned aircraft for what it calls "administrative purposes," like search-and-rescue, wildfire operations and scientific research.

"We haven't shut the door on unmanned aircraft, but there were enough complaints and incidents that we needed to, I guess you could call it, (take a) 'time out,'" Olson said.