SEOUL, South Korea – Furious about North Korea's recent nuclear test and long-range rocket launch, South Korea vows to hit back hard and says the shutdown of a jointly run factory park in the North will only be the start.
But what's next for Seoul as it looks to make its nuclear-armed northern neighbor hurt?
Some experts say South Korea's leverage began shrinking when it shut the industrial complex in Kaesong, North Korea, the last major symbol of cooperation between the rivals.
But other ways South Korea can pressure the North are being discussed.
A look at some of them:
MISSILE DEFENSE SYSTEMS
In response to North Korea's recent locket launch, Washington and Seoul have begun preparatory talks on deploying an advanced U.S. missile defense system in South Korea, despite opposition from Beijing.
Seoul says the Terminal High Altitude Area Defense, or THAAD, system would be intended to destroy North Korean missiles targeting the South. But China is worried the system could allow U.S. radars to spot missiles in its territory.
There is debate in Seoul about whether having the system is worth the fallout from angering China, South Korea's biggest trading partner.
THAAD is designed to intercept incoming targets at high altitudes midflight. The system would be useless against North Korean short-range missiles that fly at lower altitudes, and which pose the biggest immediate threat to South Korea because they could be fired quickly from mobile launchers.
Still, it would be meaningful for Seoul, which has been developing its own missile defense system to counter the North's shorter-range arsenal, to acquire multiple layers of protection as Pyongyang continues to diversify its weaponry, said Jin Moo Kim, an analyst at the government-funded Korea Institute for Defense Analysis.
TIGHTENING PORT CONTROLS
The Kaesong complex, created in 2004 during a period of rapprochement between the rivals, was the lone exception when South Korea banned all southern trade and investment to North Korea in 2010 in retaliation for the sinking of a South Korean warship that killed 46 sailors.
Seoul had already stopped joint tours to North Korea's scenic Diamond Mountain resort two years earlier, following the shooting death of a South Korean tourist by a North Korean guard.
With Kaesong now gone, perhaps for good, the last meaningful non-military option the South could take against the North would be prohibiting third-country commercial vessels from entering South Korean ports if they had previously visited North Korea, analysts say. It is unclear, however, how badly this could hurt the North.
Japan after the recent rocket launch declared a complete ban on visits by North Korean ships to Japan, something the South already does at its ports.
Experts say any new measures against North Korea need the backing of China, the North's last major political ally and by far its largest trade partner. Beijing is seen as protecting the North over fears of provoking a collapse in Pyongyang and a stream of refugees across their border.
SOUTH KOREAN NUKES?
It's difficult to imagine South Korea acquiring its own nuclear weapons to counter the North Korean threat. But the idea has entered the political debate.
Won Yoo Chul, the floor leader of President Park Geun-hye's Saenuri Party, told Parliament on Monday that the time has come for South Korea to start considering the pursuit of its own nuclear weapons program, echoing some media outlets.
Won also says the United States should bring back the tactical nuclear weapons it withdrew from South Korea in the early 1990s.
The conservative Chosun Ilbo newspaper said in an editorial last month that it's inevitable the South should begin discussions on acquiring nuclear weapons.
South Korea in previous standoffs has maintained humanitarian aid to the impoverished North, including food and fertilizer shipments. It has also supported programs by international organizations to help North Korean children and the needy.
Seoul now seems no longer willing to continue such aid.
Jeong Joon-Hee, a spokesman for Seoul's Unification Ministry, told reporters Wednesday that a temporary suspension of humanitarian exchanges is inevitable considering the severity of the North Korean threat.
South Korea has sent more than $3 billion in government and civilian aid to the North since the mid-1990s, according to President Park's office.