Seoul's forces fired around 90 machine gun rounds towards the targets and across the heavily militarized border, according to South's Yonhap news agency. The incident was triggered by ten spherical objects flying with the wind in the border area. Some of them traveled into Seoul's territory, defense ministry spokesman Moon Sang-Gyun said on Wednesday.

The military later analyzed the data, determining the objects were "balloon-like," Moon added.

Both Seoul and Pyongyang use balloons to distribute propaganda leaflets across the border. Moon ruled out the possibility of the balloons coming from the South, saying that Seoul uses cylindrical balloons, rather than spherical ones.

Previously, Yonhap cited a defense official as saying that the military fired at what could have been a drone. The object returned across the borders and disappeared from the radar, according to this official's account.

The military said it had sent a warning to Pyongyang and increased its air surveillance in response to the incident.

The rival governments remain on edge as the North escalates its nuclear program. Pyongyang also has a history of sending spy aircraft across the border. In January 2016, the military fired on a North Korean drone that flew into the demilitarized zone, and in September 2014, a South Korean fisherman found a drone that was also believed to have come from there.

Gabriel in China

Germany's Foreign Minister Sigmar Gabriel warned of "dangerous developments" in North Korea after landing in Beijing on Wednesday.

"We believe the Chinese have a big responsibility there, but we're also sure that the Chinese government is aware of that," Gabriel said at the start of his one-day diplomatic visit to China, North Korea's key ally.

Pyongyang's nuclear program is expected be among key issues as Gabriel meets with Prime Minister Li Keqiang and Foreign Minister Wang Yi later in the day.

UN Security Council vows new sanctions

The border incident came two days after Pyongyang fired a ballistic missile into the Sea of Japan. It was the second launch in just over a week and the eighth since the start of 2017.

The United Nations Security Council said on Monday it would impose additional sanctions on North Korea in response, accusing the country of "destabilizing behavior and flagrant and provocative defiance."

Members of the council vowed to better implement six rounds of sanctions already imposed against Pyongyang and demanded that the country halt its nuclear program and missile tests.

China called on "all parties to remain calm, exercise self-restraint and avoid taking provocative actions that would escalate the tensions."

The United States has urged China to use its influence over North Korea to change its behavior.

dj/jm (AFP, AP, dpa, Reuters)