South Korea is on high alert Saturday to retaliate against North Korea for any possible provocations amid a looming deadline to defuse the latest tensions on the Korean Peninsula.

North Korea has set 5 p.m. Saturday as the deadline for South Korea to halt anti-Pyongyang propaganda broadcasts along the heavily fortified border and dismantle all loudspeakers.

The North has threatened to launch "a strong military action" if South Korea defies its ultimatum. North Korea also warned late Friday that it is prepared to engage in "all-out war."

President Park Geun-hye makes comments during a surprise visit to the headquarters of Third Army in Yongin, Gyeonggi Province, on Aug. 21, 2015. (Yonhap)
The harsh war rhetoric raised tensions on the Korean Peninsula to the highest level in recent years. The two Koreas are still technically at war because the 1950-53 Korean War ended in a truce, not a peace treaty.

Cheong Wa Dae, South Korea's presidential office, plans to hold a National Security Council session around 5 p.m. to discuss countermeasures if provoked.

"We are closely monitoring the situation," presidential spokesman Min Kyung-wook said. "We are ready to strongly respond to any North Korean provocations."

A possible military clash between the two Koreas is looming large on the divided peninsula as South Korea has vowed to continue the psychological warfare, which Pyongyang claims insults its dignity.

North Korea deployed towed artillery with a 76.2 mm diameter inside the demilitarized zone that separates the two Koreas, a military source said, for its possible strike on South Korean loudspeakers that blare anti-Pyongyang messages.

"There are also moves from artillery corps in the rear area," the source said. 

The North's recent moves underscored the desperate attempt to protect what it calls the "dignity" of its leader Kim Jong-un -- a top priority among North Koreans.

South Korea has resumed the propaganda broadcasts along the border for the first time in 11 years in retaliation against North Korea for a recent landmine attack that left two South Korean soldiers severely injured.

South Korea accused the North of planting the mines inside the military buffer zone, a charge denied by North Korea.

Separately, Foreign Minister Yun Byung-se has cut short his visit to Costa Rica to deal with the escalating situations. Yun is to arrive in Seoul on early Sunday, a day ahead of schedule, according to the Foreign Ministry. (Yonhap)