Air balloons and a drone hop the border into South Korea

A suspected North Korean military drone flew over the border with South Korea. Leaflets ordering South Korea to stop broadcasting anti-North Korea propaganda were also dropped.

An unidentified object flew across the world's most guarded border into South Korea Wednesday.

It was an unpleasant surprise for South Korean troops, who fired warning shots. Yonhap News Agency reported it was a military drone operated by North Korea, just one week after a seismic event that North Korea claimed was a hydrogen bomb test

The South Korean military believes the drone was on a surveillance mission to gather intelligence on troop movements, the BBC's Kevin Kim reported, writing that, "In a country as impoverished and isolated as North Korea, drone technology is the last thing one might expect from the military." Both South Korean and US troops there have been active since last week's alleged bomb test by North Korea.

Propaganda battles have long been part of the smoldering conflict between South and North Korea, which are still technically at war, having ended the violence of the Korean War with an armistice rather than a peace treaty. In 2004, both sides toned down the propaganda in an attempt to improve relations. But since 2011, verbal assaults have flared up periodically.

South Korea has a system of 11 loudspeakers along the well-fortified border, and part of the country's immediate retaliation against the nuclear test was to turn them on, the BBC reported. North Korea has dropped leaflets via giant balloon to advertise North Korean supremacy and call for the loudspeaker voices to stop.

Such attacks may cause more consternation in North Korea than most Americans would think. In a society characterized by domineering, one-party rule, the anti-government criticism blasting from South Korean loudspeakers is a serious affront. Yet North Korea is not above its own grandstanding in the name of public relations, wrote Scott Snyder for the Council on Foreign Relations.

One wrinkle in the North Korean announcement is the seemingly desperate reach for prestige represented by the claim that the country had mastered the technology necessary to detonate a hydrogen bomb. Such a claim in the absence of conclusive corroborating evidence conveys desperation and weakness from a regime that has increasingly stood on claims to North Korea’s nuclear status as a source of domestic legitimacy. North Korea’s latest test suggests evidence of weakness rather than strength, but such a conclusion could also complicate an effective response.

The South Korean government has been unequivocal in calls for such a response, however.

"We are cooperating closely with the United States and allies to come up with effective sanctions that will make North Korea feel bone-numbing pain, not only at the Security Council but also bilaterally and multilaterally," South Korean President Park Geun-hye said in a speech, according to Reuters.

She also mentioned China's public displeasure with a North Korean nuclear program.

"I am certain that China is very well aware if such a strong will isn't followed by necessary steps, we will not be able to stop the North's fifth and sixth nuclear tests and we cannot guarantee true peace and stability," Ms. Park said, according to Reuters. "I believe the Chinese government will not allow the situation on the Korean peninsula to deteriorate further."

This report contains material from Reuters.