A suspicious drone crashed on the South Korean frontline island of Baengnyeongdo near the tense inter-Korean sea border on Monday when military tensions spiked due to North Korea’s provocative live-fire drills.

Military authorities are investigating the drone, the origin of which has yet to be verified. Observers presumed that the drone had been deployed to South Korean territory for espionage purposes.

“Around 4 p.m. on Monday, a drone crashed on the island and the military took it to investigate it and see if there are any indications of spying activities involving the drone,” a government source said, declining to be named.

The drone is said to resemble an unmanned aircraft found last Monday on a mountain in Paju, Gyeonggi Province, close to the Demilitarized Zone. Equipped with a small camera, it reportedly contains a Japanese-made engine and various Chinese parts.

Observers say that Pyongyang might have sent the drone to keep closer tabs on the South Korean military on the day when it fired some 500 artillery shells toward the South, with 100 of them falling south of the sea border, called the Northern Limit Line.

On Aug. 9, 2010, the communist state sent a drone to carry out surveillance activities near the border islands of Baengnyeongdo and Yeonpyeongdo, the same day the North fired some 100 shells toward the NLL with its coastal artillery.

Seoul officials believe that Pyongyang imported Chinese-made D-4 drones and modified them into “Banghyon” drones to fit Korean terrain features, and deployed them to frontline units.

With an operational range of 4 kilometers, the 3.23-meter-long Banghyon drone flies at an altitude of 3 kilometers at a top speed of 162 kilometers per hour. It can also carry 20-25 kilograms of explosive devices.

The North is also known to have developed and deployed unmanned aircraft for strike missions. It reportedly imported U.S.-made MQM-107D Streakers from 2010-2011 from a Middle Eastern nation, most likely Syria.

On Tuesday, the South Korean military maintained a robust readiness posture to prepare against additional North Korean provocations.

The North was seen putting together its field guns and multiple rocket launchers at the Mirim Airport in its capital of Pyongyang, indicating that it was preparing for a national-level live-fire exercise.

Experts say that Pyongyang could engage in additional provocations to show off its national pride both to the domestic and international audience during a series of national events scheduled for this month.

The North is to celebrates the “Day of Sun,” the birthday of late national founder Kim Il-sung on April 15, and the foundation of the North Korean military on April 25. The regime is also to mark when its leader Kim Jong-un became the first secretary of the North’s ruling Workers’ Party on April 11 and the first chairman of the National Defense Commission two days later.

Meanwhile, Seoul’s Defense Ministry defended its counterstrike in response to the North’s artillery barrage into South Korean waters, saying that it fired back in accordance with its principles of “rapidness, accuracy and sufficiency.”

It also said that it did not strike the origin of the North’s artillery shells, as proclaimed in its military mantra, because there were no damages to land facilities and civilian property.

After the North conducted live-fire drills, U.S. Secretary of Defense Chuck Hagel called on it to stop “dangerous” provocations and exercise restraint.

“The provocation that the North Koreans have once again engaged in is dangerous and it needs to stop,” the secretary said at a Pentagon press conference.

By Song Sang-ho (sshluck@heraldcorp.com)