Mounting tensions may have caused an exchange of artillery fire on the border between North and South Korea.
       
On Friday, North Korean troop fired two rounds toward South Korea across the demilitarized zone. South Korean troops immediately returned fire.
   
It's unclear whether the move by North Korean troops was an accident or an intentional provocation, an official at the Joint Chiefs of Staff in Seoul said. Earlier, the North vowed to retaliate against the South for its rejection of a proposal for military talks.
    
South Korean Unification Ministry spokesman Chun Hae-sung said previously arranged reunions of hundreds of families separated by the Korean War will go on as planned Saturday, despite Friday's violent exchange.

Still, the incident is a cause for concern as it comes only two weeks before South Korea prepares to host President Barack Obama and other world leaders at the Group of 20 economic summit.