North Korea again sent trash-carrying balloons into the South on Saturday, the South Korean military said, a day after Seoul warned of countermeasures against such activity.

Earlier this week, North Korea sent around 260 balloons carrying bags of trash, including waste batteries, cigarette butts and what appeared to be manure, according to the South Korean Joint Chiefs of Staff.

Authorities in Seoul condemned that act as "low-class", and the South Korean unification ministry warned Friday that the government would take countermeasures if Pyongyang did not cease such "irrational" provocations.

North Korea is "once again floating balloons carrying waste toward the South", the JCS said in a text message to reporters.

It advised the public to refrain from touching the balloons if spotted and to report them to authorities.

The Seoul city government also sent a text alert to residents on Saturday, warning of an "unidentified object presumed to be North Korean propaganda leaflets".

The object has been "detected in the airspace near Seoul and is currently being addressed by the military", it said, advising residents to "refrain from outdoor activities".

Pyongyang defended its release of the balloons earlier this week, saying the "sincere gifts" were retaliation for the balloons sent into North Korea with propaganda against leader Kim Jong Un.

North Korea has long been infuriated by the balloons sent by South Korean activists, which carry anti-Pyongyang leaflets. Sometimes, they have also sent cash, rice or USB thumb drives with South Korean drama series.

South Korean defence minister Shin Won-sik on Saturday said North Korea sending balloons with waste was "unimaginably petty and low-grade behaviour".

He added that the balloons sent into the North by activists were "humanitarian aid balloons".

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

That same year, Pyongyang, blaming the anti-North leaflets, 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.

Last year, South Korea's Constitutional Court struck down the 2020 law, calling it an undue limitation on free speech.

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