President Park Geun-hye on Wednesday visited a front-line Army unit to offer her encouragement and to call for a robust readiness posture, her office Cheong Wa Dae said, amid a spike in tensions triggered by North Korea's submarine-launched ballistic missile launch and its menacing rhetoric.

Accompanied by Defense Minister Han Min-koo and dozens of senior military and government officials, the commander-in-chief met with border troops who are participating in the ongoing annual military drills jointly conducted by South Korea and the US.

The Ulchi Freedom Guardian exercise, which Pyongyang criticizes as a rehearsal for an invasion, began its two-week run on Monday.

In an apparent protest against it, the North launched an SLBM off its east coast on Wednesday morning.

Park has recently warned that Pyongyang could launch various types of provocations, including those in cyberspace, to strengthen national unity and divert attention from its internal problems, including signs of "serious cracks" in its autocratic governing system.

It was Park's first visit to a military unit since December last year when she traveled to a unit of the Army's 28th division in Yeoncheon, some 62 kilometers north of Seoul. (Yonhap)