North and South Korea exchanged machine gun fire over their heavily guarded border on the same day that Pyongyang's leader, Kim Jong Un, who hasn't been seen in public for more than a month, failed to show at a major national ceremony.

North Korea forces opened fire a few hours after defectors living in the South launched balloons carrying propaganda leaflets denouncing the Pyongyang regime. The balloons were meant to scatter their cargo over the border, but at least one of them popped over the South. They also carried DVDs and U.S. dollar bills.

The North had warned of "catastrophic" consequences if the balloons were released. The machine gun fire fell near a South Korean base and a residential area, the Defense Ministry said, according to Yonhap. The South reportedly returned fire. There were no reports of injuries.

Jason Strother, reporting for NPR from Seoul, says the border clash comes as North Korea's Kim was a no-show at the 69th anniversary of the country's ruling Workers Party.

As The Two-Way's Krishnadev Calamur wrote on Thursday, speculation is rife over what's happened to Kim.

It's rare for the leader, whose cult of personality permeates every aspect of North Korean life, to be out of the spotlight.

Strother says: "North Korea watchers have been left to speculate on what's going on."

Journalists, analysts and officials have all weighed in with theories ranging from an illness (gout or injured ankles) to a coup against the leader, who succeeded his late father as head of the ruling dynasty in late 2011.

North Korean television has said only that Kim is suffering from "discomfort."

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