SEOUL, South Korea (AP) — Debris carried by a North Korean balloon fell on the presidential compound in central Seoul for a second time Thursday, raising concerns about the vulnerability of key South Korean sites.

The incident comes as the rival Koreas stepped up threats and rhetoric against each other over North Korea’s claims that South Korea flew drones over the capital Pyongyang this month to distribute propaganda leaflets.

No hazardous objects were found in the rubbish that fell to the ground when one of North Korea’s balloons burst over the South Korean presidential complex on Thursday morning, South Korea’s Presidential Security Service said in a statement.

North Korea has sent thousands of balloons with bags full of trash, such as plastic and paper waste, to South Korea since late May in a resumption of a Cold War-style psychological campaign. The waste that fell on the South Korean presidential compound in July also did not contain any hazardous substances.

It was not immediately known whether South Korean President Yoon Suk Yeol was at the compound during the latest incident. Later Thursday he met visiting Polish President Andrzej Duda at his office.

South Korean media reported that North Korean pamphlets criticizing Yoon and his wife, Kim Keon Hee, were found Thursday in Seoul’s Yongsan district, where Yoon’s presidential office is located. The media published photos of some leaflets describing Kim as a modern-day Marie Antoinette, the queen who was beheaded in 1793 during the French Revolution.

According to the reports, it was the first time North Korean propaganda leaflets were found in South Korea since the North began its balloon campaign five months ago.

South Korea’s presidential security service has not confirmed the reports. But South Korea’s Joint Chiefs of Staff later urged North Korea to stop distributing “crude pamphlets” defaming the South’s president, warning that Pyongyang will be fully responsible for any consequences .

Experts say North Korea likely does not have the advanced technology needed to drop balloons on specific targets.

“Whether the balloons have GPS or not, the point is to launch them in large numbers and reach the right height based on the wind direction and speed so that they can travel with that wind,” says Lee Choon Geun , honorary researcher at South That reports the Korean Institute for Science and Technology Policy.

“Although some media say that the accuracy of the balloons has improved, that improved accuracy is not because they have equipped them with some kind of guidance system, but rather because this is the season when the wind blows southward,” Lee said.

North Korea accused South Korea of ​​using drones to drop propaganda leaflets over Pyongyang this month and threatened a military response if it happened again. South Korea has refused to confirm whether it has sent drones, but warned that North Korea faces the end of its regime if the safety of South Korean citizens is threatened.

North Korea said its balloon activities were a tit-for-tat move against South Korean activists who launched anti-Pyongyang leaflets via their own balloons. South Korea responded by restarting propaganda loudspeaker broadcasts in border areas, prompting North Korea to turn on its own frontline loudspeakers.

Korea’s Cold War-style campaigns come as North Korean leader Kim Jong Un has stepped up the pace of his weapons tests and expanded military cooperation with Russia.

U.S. and South Korean officials said Wednesday that 3,000 North Korean troops have been deployed to Russia and are training in various locations. South Korean officials say North Korea eventually wants to send a total of 10,000 troops to Russia to support its war efforts in Ukraine.

South Korea is concerned that Russia will reward North Korea by giving it advanced technologies that could improve the North’s nuclear and missile programs aimed at South Korea and the United States.