SEOUL, South Korea — North Korea plans to resume anti-Seoul propaganda broadcasts along the heavily armed border with South Korea, leader Kim Jong Un's sister said, reviving a psychological warfare campaign as tensions rise after land mine blasts injured three South Korean front-line soldiers.Kim Yo Jong, her brother's top spokesperson on Washington and Seoul, made the announcement Wednesday after visiting front-line areas where North Korean troops are reinforcing the border.She renewed a threat to retaliate against any South Korean provocation aimed at the fortification work.In a follow-up statement Thursday, she said the North would place "new counter means" on alert along the border and have its loudspeakers on "standby" within days.North Korea has been adding mines, barbed wire fences, anti-tank barriers and other fortifications to what's already one of the world's most heavily armed borders as Kim Jong Un pushes a hard line toward Seoul.Touring the area with Marshal Pak Jong Chon, one of her brother's top military officials, Kim Yo Jong called the fortification work a "sacred and great undertaking" supporting the leader's policy of permanently severing ties with South Korea, which he has declared his most hostile adversary amid a broader diplomatic stalemate with Washington."Our tactical hunting teams are taking new positions, and within October, the loudspeakers for psychological warfare against the ROK will be in operation along the whole border," Kim Yo Jong said, using the initials of South Korea's formal name, the Republic of Korea.She warned that if South Korean warning shots — which Seoul says are meant to force North Korean soldiers doing fortification work back across the border — cause "actual harm to our territorial security and our service persons' safety," North Korean border guards "will show no mercy for the armed gangsters bereft of reason."Asked about Kim Yo Jong's threat to resume the loudspeaker broadcasts, South Korean Defense Ministr...