S. Korea shells North after rocket attack

South Korean artillery units fired dozens of shells into North Korea on Thursday in response to a rocket fired over the heavily-militarised frontier, as both sides pushed already elevated cross-border tensions to dangerously high levels. North Korea followed up with an ultimatum sent via military hotline that gave the South 48 hours to dismantle loudspeakers blasting propaganda messages across the border or face further military action. Thursday's incident came amid heightened tensions following