Seoul, South Korea: South Korea’s military said an unidentified object that flew across the border from rival North Korea and prompted the South to respond with warning shots on Tuesday was probably a balloon carrying Pyongyang’s propaganda leaflets.

An official from the Defence Ministry said Wednesday that the military concluded that the object was most likely a balloon after analysing information from radar and observation equipment. The official didn’t want to be named, citing office rules.

South Korea’s Joint Chiefs of Staff in a statement on Tuesday said the military broadcast a warning to North Korea in response to the object before firing the warning shots, and also that the military bolstered its air surveillance.

South Korea’s Yonhap news agency, without citing a source, reported that the South fired about 90 machine gun rounds into the air and toward North Korea. Local media had speculated the object was a North Korean military drone. North Korea often uses balloons to fly propaganda leaflets to the South.

There was no immediate comment in North Korea’s state-run media, and no reports that the North had returned fire.

The Koreas face off across the world’s most heavily armed border, and their militaries occasionally clash. North Korea is also building nuclear-tipped missiles and has greeted new South Korean President Moon Jae-in, who wants to reach out to the North, with two missile test-launches, part of a flurry of tests since leader Kim Jong-un took over in late 2011.

In 2014, soldiers exchanged machine gun and rifle fire after South Korean activists released anti-North Korean propaganda balloons across the Demilitarised Zone, but no casualties were reported.

In January 2016, South Korea’s military fired warning shots after a North Korean drone briefly crossed the border.