Story highlights Three diminutive single-engine unmanned propeller planes were found in March and April

They look like hobby shop model airplanes with consumer cameras shoved into them

They don't have strong military or spy capabilities, but they made it through air defenses

Spring is typically a time of high provocations between North and South Korea

Call them drones; call them toy airplanes with digital cameras dropped into their girths.

Either way, South Korean defense officials said on Friday they were sure that they came from North Korea and that they were up to no good.

Three diminutive single-engine unmanned propeller planes that look like they could have come from a hobby shop were found on the ground in March and April in parts of the South near the border with the northern Communist regime.

Though the low-tech buzzers don't seem to represent a major danger, they come in the shadow of North Korean missile launches and the impending countdown to the test of a nuclear device.

And they made it through South Korean air defenses.

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Ministry of National Defense officials in Seoul immediately suspected that the sky-blue colored fliers belonged to Pyongyang. They formed an investigation team with the United States in mid-April to analyze the "travel log file" and photos taken by the drones and announced the results on Friday.

Scientists found a "smoking gun that all three were sent from North Korea and are programmed to return to North Korea," South Korean defense spokesman Kim Min-soek said.

Photos the drones took along on their journey corroborate their flight path, he said.

Precarious cargo

Had the mechanical carrier pigeons made it back home, they would have delivered precarious cargo, but it would have been far from precious.

Japanese-made digital cameras, which look like they could be of the consumer variety, were inserted into the bellies of the drones and had taken aerial photos of the South from around the border region.

All three were programmed to fly over military facilities, and two of them had images of targets of military interest -- strategically important islands near the demilitarized zone, and the Blue House, residence and office of South Korea's President Park Geun-hye.

Images from the third drone were not available to South Korean investigators. A wild ginseng digger had stumbled upon the plane and had deleted its memory card so he could use it himself, the Korea Times reported.

The planes were not capable of transmitting images back to North Korea in real time, and the photos themselves were no better than what one might see on a service akin to Google Earth, Kim said in a previous briefing.

Limited capabilities

There is little danger the drones could have made it far into South Korea.

The type of drone is not used for long-range missions, a defense analyst said. Instead they're better suited to see what the enemy is up to on the other side of a hill or wall.

"It has quite a small range, it doesn't have very long endurance so it would only be up there for a few hours. You would use those to see what the other guys are doing in a battlefield environment," said James Hardy, the Asia Pacific editor of IHS Jane's Defence Weekly magazine.

"They're very much closely built off a remote-controlled aircraft that you can buy in a toy store. They're just a militarized version of that," Hardy said.

The Korean drones are nowhere near as sophisticated as those used by the United States in Pakistan, Yemen and Afghanistan, he said.

They would also not make much of a weapon, if someone decided to stuff explosives into them, Kim has said.

"Even if they are to be used for future attacks, (they) can only carry 2-3 kilograms of TNT and cannot cause huge damage."

North Korea has flaunted similar, larger UAVs at military parades in recent years, and some of them have been spiked with explosives, Hardy said.

Video footage shows North Korean exercises using them as missiles, but it's an expensive way to build a bomb, he said. And it could only take out a single vehicle or ship.

'Tis the season

Spring is traditionally a time of high tensions between Pyongyang on the one side and Seoul and Washington on the other.

Annual U.S.-South Korean joint military drills, that ended on April 7, drew criticism from North Korea, which views the exercises as "dress rehearsals for invasion," according to analyst James Person from the Woodrow Wilson Center.

In March, Pyongyang fired two mid-range ballistics missiles off its eastern coast, in an apparent response to the drills. Days later, the two sides fired hundreds of shells across the Northern Limit Line, their disputed maritime border.

The shells were shot into the sea, not at hard targets.

North Korea also warned it was preparing to test another nuclear device.

"It's all good stuff because it allows the North Koreans to do something provocative and slightly annoying which might embarrass South Koreans, but it's not provocative enough to create a proper military response," Hardy said.

Slipping through

The drones would fit well into that category, since they slipped through South Korean air defenses.

They are made of polycarbonate, which is difficult to detect with radar, according to South Korea's Yonhap news agency.

They fly at an average speed of about 110 km per hour (68 mph) at an altitude of 1.3 km (.8 miles).

They were launched in North Korea from three locations, South Korea's defense ministry said: Near the Kaesong area, 27 kilometers southeast of Haeju and 17 kilometers from Pyonggak.

South Korea's defense ministry called the intrusion by the drones a violation of the truce that ended the bloody conflict between North and South Korea in 1953.

Kim said Seoul will send a warning via the United Nations to Pyongyang and tighten air defenses as a response to the drones.