North Korea is reportedly dismantling a North-South rail link once seen as vital to restoring commerce between the two Koreas on the road to inter-Korean rapprochement and reconciliation.

South Korea’s National Intelligence Agency reports “parts of the track” that runs from a modern station near the east coast of the South “are being demolished” after the line crosses the demilitarized zone into North Korea. Presumably the line, built at South Korea’s tremendous expense more than 20 years ago, appears marked for destruction on the northern side, which could use the tracks for construction projects.

A similar fate is likely for another railroad linking South to North on the west side of the peninsula. That line goes to the former Kaesong industrial zone, built by South Korea but taken over by the North in 2013. North Korea refused to agree on freight or passenger service on either line after welcoming the prospect of opening rail traffic up and down the Korean peninsula for the first time since the Korean War.

The report of the beginning of the dismantling of the rail line inside North Korea was the latest sign of rapidly rising tensions between North and South Korea. The North Korean leader, Kim Jong-un, has said South Korea is an “enemy” with which there’s no point in seeking peaceful unification — or even a peace agreement in place of the truce that ended the Korean War in 1953.

Mr. Kim has also barricaded two roads that were occasionally used between the two Koreas — and is believed to have mined both roads with explosives capable of blowing up heavy vehicles, including tanks.

Most recently, North-South relations were aggravated by North Korea launching hundreds of balloons laden with trash, including manure, that cascaded into South Korea. The South’s President Yoon Seok-yul, in a speech Thursday on the South’s Memorial Day, called the North’s balloon launches “despicable” and vowed his government would “never overlook the threat from North Korea.”

He spoke two days after the South nullified a “comprehensive military agreement” reached by his left-leaning predecessor, Moon Jae-in, in a summit with Kim Jong-un more than six years ago for suspending military operations close to the demilitarized zone, including reconnaissance flights.

The South’s Yonhap News Agency reported military sources saying exercises would resume next week along the DMZ and also around South Korean islands close to North Korea in the Yellow Sea.

Meanwhile, South Korean activists, mostly defectors from North Korea,  challenged the North by another barrage of leaflets that authorities had to have quietly approved. 

A noted defector-activist, Park Sang-hak, organized the launch of balloons carrying pamphlets castigating the Kim dynasty beginning with Kim Jong-un’s grandfather, Kim Il-sung, installed by the former Soviet Union right after the Japanese surrender in 1945.

The balloons also carried USB sticks carrying South Korean movies and K-Pop that North Koreans love despite risks of torture, imprisonment and even death for viewing and listening to them.

Leader of a group called Fighters for a Free Korea, Mr. Park was banned from firing leaflets during the Moon administration but has launched them a number of times over the years in defiance of attempts to stop him. North Korea fired off balloons carrying trash in direct response to one of Mr. Park’s balloon barrages.

More significantly militarily, an American B-1 bomber flew over South Korea for the first time in seven years. South Korean fighter planes escorted the B-1 in a display likely intended to remind Kim Jong-un of the consequences he might face if he dares make good on his bold threats to fire missiles against the South.

Mr. Yoon in his speech reminded South Koreans of the close ties he’s formed with Washington, “building upon the more robust ROK-U.S. alliance and cooperation with the international community.”