OTTAWA -- Publicity about near-misses between drones and passenger aircraft might give terrorists ideas about how to take down a plane, a federal intelligence report warns.

The Transport Canada report obtained by The Canadian Press also suggests small unmanned aerial vehicles, or UAVs, could easily be used for advance surveillance of targets.

The report tempers such fears by noting the practical hurdles in employing a drone for nefarious purposes.

But the assessment underscores concern in intelligence circles that terrorists could take advantage of the tiny, inexpensive and widely available flying machines.

The report documents five reports of "near misses" between Canadian aircraft and UAVs last year. In September 2015, a WestJet flight from Edmonton to Abbotsford, B.C., reported a drone passing about 60 metres underneath the plane.

Just last month, a Porter Airlines fight to Toronto narrowly avoided crashing into an object initially thought to be a drone.

Media coverage of near-collisions between UAVs and passenger aircraft "may encourage interest amongst extremists to consider the tactic," the Transport Canada intelligence report says.

However, given the short flying time -- 10 to 40 minutes -- of most off-the-shelf drones and strong, persistent winds at high altitudes, "intentionally striking an aircraft in-flight would be unlikely," the report adds.

A heavily censored version of the secret January 2016 report was released under the Access to Information Act.

Extremist use of a drone is "certainly not impossible and the authorities are not necessarily exaggerating things here," said Jez Littlewood, a terrorism expert at the Norman Paterson School of International Affairs at Carleton University.

But given the current state of the technology, Canadians shouldn't panic about the notion of a commercially available drone being used to ram into an aircraft, he said.

Using a store-bought drone to carry and drop a bomb would also be challenging, and extremist groups tend to gravitate to more readily available weapons, Littlewood added.

In recent years the United States has launched hundreds of armed drone strikes to kill what it says are thousands of terrorist combatants.

But UAVs are also used for a variety of peaceful applications including agricultural surveys, police investigations, meteorology, search and rescue, and movie shoots -- as well as by hobbyists with an ever-expanding choice of models.

"We judge that Canada-based extremists could easily obtain a UAV to conduct reconnaissance on transportation targets or infrastructure," the Transport Canada intelligence report says. "However, using a UAV for this purpose would draw attention to potential attack planning."

For example, the report notes, in May last year the marine security officer of a dock in the port of Nanaimo, B.C., advised Transport Canada that employees saw a drone flying around the port in a suspicious manner and that they believed it was taking photos.

In 2014, internal RCMP documents noted there had been several extremist plots around the globe -- none successful -- to use drones in attacks involving explosives, chemical weapons or biological agents.

There are four terrorist groups with identifiable drone programs -- Hezbollah, Hamas, the Islamic State of Iraq and the Levant, and Jabhat Fateh al-Sham, all of whom are primarily active in the Middle East, says a recent report by the Combating Terrorism Centre at the U.S. West Point military academy.

It cites a report of Hezbollah dropping two small bombs from what was believed to have been a modified, commercially available drone over rebel positions in Syria as a possible watershed event that could represent the "leading edge of a wave of similar incidents that could follow in the months, years and decades ahead."