North Korea said Sunday it would stop sending trash-filled balloons across the border into the South, saying the "disgusting" missives had been an effective countermeasure against propaganda sent by anti-regime activists.

Since Tuesday, the North has sent nearly a thousand balloons carrying bags of rubbish containing everything from cigarette butts to bits of cardboard and plastic, Seoul's military said, warning the public to stay away.

South Korea has called the latest provocation from its nuclear-armed neighbor "irrational" and "low-class" but, unlike the spate of recent ballistic missile launches, the trash campaign does not violate UN sanctions on Kim Jong Un's isolated regime.

Seoul on Sunday warned it would take strong countermeasures unless the North called off the balloon bombardment, saying it runs counter to the armistice agreement that ended the 1950-53 Korean War hostilities.

Late Sunday, the North announced it would stop its campaign, after scattering what it claimed was "15 tons of waste paper" using thousands of "devices" to deliver them.

"We have given the South Koreans a full experience of how disgusting and labor-intensive it is to collect scattered waste paper," it said in a statement carried by the official Korean Central News Agency. 

The North said it will now "temporarily suspend" its campaign, saying it had been a "pure countermeasure".

"However, if the South Koreans resume the distribution of anti-DPRK leaflets, we will respond by scattering one hundred times the amount of waste paper and filth, as we have already warned, in proportion to the detected quantity and frequency," it said, using the acronym for the country's official name.

Activists in the South have also floated their own balloons over the border, filled with leaflets and sometimes cash, rice or USB thumb drives loaded with K-dramas.

Earlier this week, Pyongyang described its "sincere gifts" as a retaliation for the propaganda-laden balloons sent into North Korea.

South Korea's Joint Chiefs of Staff said the balloons had been landing in northern provinces, including the capital Seoul and the adjacent area of Gyeonggi, which are collectively home to nearly half of South Korea's population. 

The latest batch of balloons were full of "waste such as cigarette butts, scrap paper, fabric pieces and plastic," the JCS said, adding that military officials and police were collecting them.

"Our military is conducting surveillance and reconnaissance from the launch points of the balloons, tracking them through aerial reconnaissance, and collecting the fallen debris, prioritizing public safety," it said.

Balloon wars

South Korea's National Security Council met Sunday, and a presidential official said Seoul would not rule out responding to the balloons by resuming loudspeaker propaganda campaigns along the border with North Korea.

In the past, South Korea has broadcast anti-Kim propaganda into the North, which infuriates Pyongyang.

"If Seoul chooses to resume anti-North broadcast via loudspeakers along the border, which Pyongyang dislikes as much as anti-Kim balloons, it could lead to limited armed conflict along border areas, such as in the West Sea," said Cheong Seong-chang, director of the Korean peninsula strategy at Sejong Institute. 

In 2018, during a period of improved inter-Korean relations, both leaders agreed to "completely cease all hostile acts against each other in every domain", including the distribution of leaflets.

South Korea's parliament passed a law in 2020 criminalizing sending leaflets into the North, but the law -- which did not deter the activists -- was struck down last year as a violation of free speech.

Kim Jong Un's sister Kim Yo Jong -- one of Pyongyang's key spokespeople -- mocked South Korea for complaining about the balloons this week, saying North Koreans were simply exercising their freedom of expression.

The two Koreas' propaganda offensives have sometimes escalated into larger tit-for-tats. 

In June 2020, Pyongyang unilaterally cut off all official military and political communication links with the South and blew up an inter-Korean liaison office on its side of the border.

The trash campaign comes after analysts have warned Kim is testing weapons before sending them to Russia for use in Ukraine, with South Korea's defense minister saying this weekend that Pyongyang has now shipped about 10,000 containers of arms to Moscow, in return for Russian satellite know-how.