South Korea's president on Monday vowed a hard line and signaled Seoul's mounting frustration as marathon negotiations by senior officials from the rival Koreas stretched into a third day.

Park Geun-hye said that without a clear North Korean apology for a land mine attack that maimed two soldiers, anti-Pyongyang propaganda broadcasts will continue. Her strong words provide a good hint at why the talks, which started Saturday evening and whose second session began Sunday afternoon and was still going Monday afternoon, have dragged on.

For now, the try at diplomacy has pushed aside previous heated warnings of imminent war, but South Korea's military said North Korea has continued to prepare for a fight, moving unusual numbers of troops and submarines to the border.

North Korea has denied involvement in the land mine explosions earlier this month and rejected Seoul's report that Pyongyang launched an artillery barrage last week -- so winning an apology will be difficult work. Pyongyang demands that Seoul stop the propaganda broadcasts started in retaliation for the land mine attack.

These are the highest-level talks between the two Koreas in a year. And just the fact that senior officials from countries that have spent recent days vowing to destroy each other are sitting together at a table in Panmunjom, the border enclave where the 1953 armistice ending fighting in the Korean War was agreed to, is something of a victory.

The length of the talks -- nearly 10 hours for the first session and more than 21 for the second -- and the lack of immediate progress are not unusual. While the Koreas often have difficulty agreeing to talks, once they do, overlong sessions are often the rule. After decades of animosity and bloodshed, however, finding common ground is much harder.

President Park said during a meeting with top aides that Seoul would not "stand down even if North Korea ratchets up provocation to its highest level and threatens our national security."

She said Seoul needs "a definite apology" and a promise that such provocations would not recur.

The decision to hold talks came hours ahead of a Saturday deadline set by North Korea for the South to dismantle the propaganda loudspeakers. North Korea had declared that its front-line troops were in full war readiness and prepared to go to battle if Seoul did not back down.

South Korea said that even as the North was pursuing dialogue, its troops were preparing for battle.

An official from Seoul's Defense Ministry said that about 70 percent of the North's more than 70 submarines and undersea vehicles had left their bases and were undetectable by the South Korean military as of Saturday. The official, who refused to be named because of official rules, also said the North had doubled the strength of its front-line artillery forces since the start of the talks Saturday evening.

South Korean military officials wouldn't confirm or deny but seemed to cast doubt Monday on a Yonhap news agency report, citing unidentified military sources, that said North Korea had moved toward the border about 10 hovercraft used for landings by special operation forces in the event of a war. Defense Ministry spokesman Kim Min-seok said the truth is "a bit different" than what was reported but wouldn't provide further details.

The standoff started with the explosions of land mines on the southern side of the Demilitarized Zone between the Koreas that Seoul says were planted by North Korea. In response, the South resumed anti-Pyongyang propaganda broadcasts for the first time in 11 years, infuriating the North, which is extremely sensitive to any criticism of its authoritarian system. Analysts say the North fears that the broadcasts could demoralize its front-line troops and inspire them to defect.

On Thursday, South Korea's military fired dozens of artillery rounds across the border in response to what Seoul said were North Korean artillery strikes meant to back up an earlier threat to attack the loudspeakers.

The Defense Ministry official said the South continued the anti-Pyongyang broadcasts even after the start of the talks Saturday and also after the second session began Sunday. He said Seoul would decide after the talks whether to halt the broadcasts.

While the meeting offered a way for the rivals to avoid an immediate collision, analysts in Seoul wondered whether the countries were standing too far apart to expect a quick agreement.

South Korea probably can't afford to walk away with a weak agreement after it had openly vowed to stem a "vicious cycle" of North Korean provocations amid public anger over the land mines, said Koh Yu-hwan, a North Korea expert at Seoul's Dongguk University.

At the meeting, South Korea's presidential national security director, Kim Kwan-jin, and Unification Minister Hong Yong-pyo sat down with Hwang Pyong So, the top political officer for the Korean People's Army, and Kim Yang Gon, a senior North Korean official responsible for South Korean affairs. Hwang is considered by outside analysts to be North Korea's second most important official after supreme leader Kim Jong Un.

In Pyongyang, North Korean state media reported that more than 1 million young people have volunteered to join or rejoin the military to defend their country should a conflict break out.

Despite such highly charged rhetoric, which is not particularly unusual, activity in the North's capital remained calm on Sunday, with people going about their daily routines. Truckloads of soldiers singing martial songs could occasionally be seen driving around the city, and a single minivan with camouflage netting was parked near the main train station.

Instead of anxiously awaiting the outcome of the talks, many Pyongyang residents were riveted to TVs in public places to watch the debut of the "Boy General" cartoon show, which has been revamped for the first time in five years at the order of Kim Jong Un.