SEOUL, Oct 22 - North Korea will place anti-South Korea loudspeakers on standby along the entire border within days and has put new countermeasures on alert, Kim Yo Jong, the powerful sister of North Korea's leader, said on Thursday, warning Seoul of "the most horrible and distressing situation" if it continues what Pyongyang calls interference.

The threats to redeploy propaganda loudspeakers, announced in Kim’s second statement within hours, risk reversing South Korean President Lee Jae Myung’s signature gains in easing inter-Korean tensions and pushing tensions along the heavily fortified frontier to their highest level since he took office.

In a statement carried by state media KCNA, Kim said she was responding to a special adviser to Lee on defence policy, who accused North Korea of planting mines that wounded South Korean soldiers and told it not to escalate tensions with loudspeaker broadcasts.

"Our new counter means will get into the alert for duty at all the southern border line and the loudspeakers against the ROK will be on standby in a matter of days,” she said. She said North Korea would continue fortifying its southern border.

On Wednesday evening, Kim said North Korea would activate anti-South Korea loudspeakers across the border by the end of October after visiting fortification sites with senior military officials.

South Korea says North Korean mines caused a border blast last month that seriously wounded two soldiers. North Korea denies responsibility, calling the incident a South Korean fabrication.

Lim Eul-chul, a professor at Seoul's Kyungnam University, said Kim's warnings did not necessarily mean the loudspeakers would be activated.

But they present Lee's administration with an "enormous dilemma", he said, as it faces a choice between pursuing its policy of peaceful engagement and containing aggressive North Korean military activity along the border.