South Korea on Sunday resumed a loudspeaker propaganda campaign against the North after Pyongyang sent a fresh barrage of trash-filled balloons across the border.

Relations between the two Koreas are at one of their lowest points in years and in recent weeks the two have engaged in a tit-for-tat campaign of balloon launches, with analysts warning the escalatory cycle could end in actual military skirmishes.

Seoul this month suspended a 2018 military deal aimed at reducing tensions on the peninsula after Pyongyang sent hundreds of balloons carrying bags of garbage, including cigarette butts and plastic waste, paving the way for the resumption of the use of loudspeakers along the border.

Seoul has slammed the balloon launches as "low class" but, unlike Kim Jong Un's repeated ballistic missile tests, they do not violate rafts of UN sanctions on the nuclear-armed North.

"The South Korean military conducted a loudspeaker broadcast this afternoon," Seoul's Joint Chiefs of Staff said, adding that whether additional broadcasts follow "depends entirely on North Korea's actions."

The president's office had earlier confirmed the move, describing it as "corresponding measures" for the more than 300 trash-filled balloons Pyongyang sent across the border in a fresh blitz that started on Saturday.

"Although the measures we are taking may be difficult for the North Korean regime to endure, they will deliver messages of light and hope to the North Korean military and citizens," it said.

Activists in the South have floated dozens of balloons bearing K-pop, dollar bills and anti-Kim Jong Un propaganda northwards in recent weeks, infuriating Pyongyang which has retaliated in kind.

Pyongyang sent nearly a thousand balloons across the border in late May and early June before calling off its campaign. It restarted on Saturday in response to new launches last week by the activists, against which Seoul's government has almost no legal recourse.

The Seoul city government, as well as officials in surrounding Gyeonggi province, sent out a text alert to residents on Saturday warning about the new balloons.

"North Korea is making another low-class provocation with trash balloons against our civilian areas," Seoul mayor Oh Se-hoon wrote in a Facebook post.

Seoul's military said an "analysis shows there were no substances that were harmful to safety", with the latest batch of balloons containing waste paper and plastic. However, it warned the public to stay away and report any balloons to authorities. 

 Low point in ties 

 Seoul's decision to resume the loudspeaker broadcasts could have serious implications, experts said, with previous propaganda tit-for-tats having had real-world consequences for inter-Korean relations.

The loudspeaker broadcasts, a tactic which dates back to the 1950-1953 Korean War, infuriate Pyongyang, which has previously threatened artillery strikes against the loudspeaker units unless they were switched off.

"There is a high possibility the resuming of speakers could lead to an armed conflict," Cheong Seong-chang, director of the Korean peninsula strategy at Sejong Institute, told AFP.

"With the resuming of the speakers, North Korea will not stay put. It is likely that North Korea will resume firing in the West Sea or fire at the balloons if the South sends any again," Cheong said.

"North Korea has been jamming GPS signals for several days last week and it is likely for this kind of provocation to appear in a much stronger form in the West Sea as well."

In 2018, during a period of improved inter-Korean relations, the leaders of the two Koreas agreed to "completely cease all hostile acts", including stopping the leaflets.

The South Korean parliament passed a law in 2020 criminalising the act of sending leaflets to the North, but the activists did not stop and the law was struck down by the Constitutional Court last year as an undue limitation on free speech.

The opposition Democratic Party criticised the government for not doing more to stop the activists' balloons, with a spokesperson at a Sunday briefing saying they were using "'freedom of expression' as an excuse to jeopardise the safety of our people".

They also said the resumption of loudspeaker campaigns was not wise, adding "the government's move poses a risk of escalating into a regional war".