HUNCHUN, China – The warning came from Kim Jong Un, the North Korean ruler who sees his isolated nation, just across the border from this busy Chinese trading town, as under siege.

“We must extend the fight against the enemy’s ideological and cultural infiltration,” Kim said in an October speech at the headquarters of his internal security service. Kim, who became North Korea’s supreme leader after the death of his father a year ago, called upon his vast security network to “ruthlessly crush those hostile elements.”

Over the past year, Kim has intensified a border crackdown that has attempted to seal the once-porous 880-mile frontier with China, smugglers and analysts say.

The assault that he fears? It’s being waged with cheap televisions rigged to receive foreign broadcasts, and with smuggled mobile phones that — if you can get a Chinese signal along the border — can call the outside world. Very often, it arrives in the form of wildly popular South Korean soap operas smuggled in on DVDs or computer thumb drives.

In North Korea, a country where international phone calls and Internet connections exist only for a tiny fraction of a tiny elite, and televisions and radios must be permanently preset to receive only state broadcasts, it’s Korean-language TV heartache they crave.

“South Korean dramas, that’s what everyone wants,” grumbled a Seoul-based Christian missionary who runs a string of safe houses in this part of China, where his network helps people living underground after fleeing North Korea. One safe house is reserved for traders who sell everything from electronics to shoes inside North Korea — and who smuggle everything from Bibles to soap operas on the side.

There’s “Autumn in My Heart,” a 12-year-old tear-jerker replete with switched babies, forbidden love and a comatose heroine. And “Stairway to Heaven,” an epic of more forbidden love, more switched identities, blindness, insanity, a brain tumor and an evil stepmother.

But if it looks absurd — a Stalinist nation vowing to crush an assault of bad lighting and overacting — the dilemma is deadly serious for Kim, who needs to find a way to modernize his country and its economy while holding on to absolute power.

Today, changing technologies, ambitious smugglers and well-funded critics of North Korea mean that everything from DVD melodramas to illegal Chinese cellphones to Korean-language radio news broadcasts funded by the U.S. government make their way into North Korea. Their presence exposes an ever-growing number of North Koreans to the outside world and threatens the underpinnings of the Kim regime.

Kim’s crackdown has been largely aimed at the border with China, long the route for much of the outside information making its way into North Korea, as well as for refugees trying to get out.

Entire border-security units have been replaced inside North Korea, fences have been strengthened and punishments ramped up for anyone caught trying to get through, according to smugglers, analysts and Chinese with family ties across the border.

“There is substantial demand” for things like South Korean movies and television programs, said Nat Kretchun, associate director of international consulting group InterMedia, which released a report earlier this year about information flow into North Korea, based on surveys of hundreds of recent North Korean defectors. The study was commissioned by the U.S. State Department.

People are more willing to watch foreign movies and television programs, talk on illegal mobile phones, and tell family and friends about what they are doing, said Kretchun.

For now, though, times are tough along the border, with smugglers saying North Korean guards have become far stricter about searching for contraband.

The enemy works out of places like Hunchun, a brutally cold, money-hungry border town of car-parts shops, cavernous indoor markets piled with shiny polyester clothing and off-brand electronics so cheap it seems almost impossible. Just a few miles from both North Korea and Russia, it’s a town where nearly all signs are in three languages — Chinese, Korean and Russian — and where you can find a smuggler in just a few phone calls. Even if they rarely give a name, and are often identified only by their mobile-phone numbers.

North Korean viewers living in tiny two-room homes and struggling to feed their families can see houses with bedrooms just for children, and dinners with endless food. They see everyday people casually complaining about policemen and politicians. Scenes like that are provocative in a country where defectors say criticizing the ruling elite can send entire families to sprawling prison camps, and where bicycles are considered luxury items for many.

Plenty of smugglers are willing to carry South Korean DVDs and other highly forbidden contraband.

Millions of foreign TV and movie recordings are thought to be floating around North Korea, though they are most easily available in cities near the Chinese border. With the crackdown, analysts say smugglers appear to have shifted to new techniques, at least for videos: carrying recordings on tiny thumb drives, and then transferring the programs to DVDs inside North Korea.

North Korea has been trying — albeit haltingly and slowly — to revitalize its barely functioning economy and crack open a door to the outside. Foreign tourists are now commonplace in Pyongyang, though on tightly controlled trips, and Kim has told his people that they should never go hungry again. Western movies occasionally are shown on state television. North Korean officials now actively court foreign investors.

As a result, North Korea has found itself flirting with modernity — more than a million of the 24 million North Koreans now have mobile phones, for instance, though they can place and receive calls only domestically — while trying desperately to keep a tight grip on the public.

“They want to modernize, but the cost of this effort is information, which could easily destabilize the regime,” said Victor Cha, former director for Asian affairs at the National Security Council in the George W. Bush administration, and now a professor at Georgetown University. “Without control of information, there is no regime.”