President Donald Trump is raising pressure on North Korea, touting the US naval "armada" he ordered to the troubled peninsula and promising America will "solve the problem" if China won't help.
He wants to stop Pyongyang from developing a long-range nuclear missile, but North Korean leader Kim Jong-un sees such a weapon as key to his regime's survival.
The situation has the makings of a stand-off, with Kim expected to conduct another nuclear test soon, and Washington aware that any military action would trigger an unknowable set of potentially catastrophic consequences.
Still, the Trump administration has been forceful in its warnings to North Korea that leave military options "on the table," as Secretary of State Rex Tillerson put it.
The threat carries extra weight after Trump's strike on a Syrian air base last week.
- What is America's military presence? -
The United States currently has about 28,500 troops stationed in South Korea, a legacy from the armistice at the end of the Korean War, along with multiple squadrons of F-16 fighters and A-10 ground-attack jets.
The American forces are closely intertwined with their South Korean partners and the two militaries conduct annual drills together.
A defining mantra for US forces in South Korea is that the risk of war is ever-present so they should always be ready to "fight tonight."
While training is supposedly of a defensive nature, US and Asian press have recently published excerpts of a secretive plan that supposedly lays out a pre-emptive strike on North Korea.
Additionally, another 50,000 US troops are stationed in Japan.
- An American 'armada' -
"We are sending an armada. Very powerful," Trump said Wednesday. "We have submarines. Very powerful. Far more powerful than the aircraft carrier."
He was referring to a strike group headed by the USS Carl Vinson supercarrier that has been re-routed to the Korean peninsula in a show of force against Kim.
The strike group, which deployed with about 6,500 sailors, is still some way south, conducting exercises with the Australian navy.
The US Navy already has a massive regional presence, including another carrier strike group headquartered at Yokosuka in Japan.
The US territory of Guam, a few hours away by plane, is home to stealthy B-2 bombers.
- Can the US stop a missile? -
The United States, South Korea and Japan have established an advanced regional missile-defense system that should be able to take out a North Korean rocket.
The US military last month begun deploying the Terminal High Altitude Area Defense (THAAD) system to South Korea, capable of destroying short, medium and intermediate-range missiles in their final phase of flight.
The move infuriated China, which has argued the deployment would further destabilize the situation on the Korean peninsula.
The US and its allies also have the Aegis Ballistic Missile Defense System at their disposal, along with Patriot Advanced Capability-3 interceptor batteries.
Japan has four destroyers using the Aegis system and 17 of these latest Patriot batteries. South Korea has an older variant of the Patriot.
- Do these work? -
No system is infallible and the combined missile defenses do not provide perfect protection.
North Korea experts Michael Elleman and Michael Zagurek Jr wrote on the 38 North blog that the THAAD and Patriot system would "substantially enhance South Korea's capacity to minimize the damage caused by a large North Korean missile attack."
"However, it is important to note that a layered defense will not be able to completely block such an attack. As a result, missiles armed with nuclear weapons could cause significant casualties as well as damage in the South."
According to a study by the conservative Heritage Foundation think tank, experts believe Pyongyang probably has 10?16 nuclear weapons, and the cache could swell to as many as 100 within the next few years.
It is possible the regime may already have succeeded in miniaturizing a warhead capable of being attached to a Nodong missile that could reach Japan.
- What about a warning shot? -
There is no "easy" way to back up the threat of military action with a low-level or limited strike such as that conducted last week in Syria against a regime air base.
"The administration knows any kind of military attack on North Korea could lead to a North Korean military response and even perhaps an all-out conflict on the peninsula -- and that would be hundreds of thousands of casualties," Bruce Klingner, a senior research fellow at the Heritage Foundation, told AFP.
"Certainly the consequences of any military action could be dire. North Korea is not Syria."
Anthony Ruggiero, a senior fellow and North Korea expert at the Foundation for Defense of Democracies, thinks cooler heads will prevail.
Ultimately, Kim is rational enough to understand that a missile attack on the South would spell the end for his regime.
"His ultimate goal is regime survival ... and that would be close to suicide for him," Ruggiero told AFP.