South Korea's military launched a volley of ballistic missiles simulating an attack on the North's nuclear test site Monday as the US warned it could launch a "massive military response" to threats from Pyongyang amid efforts by Japan to defend itself.
In an exercise responding to a test of what Pyongyang says was a hydrogen bomb, South Korean short-range Hyunmoo ballistic missiles roared into the sky in the pale light of dawn from a launch site on the country's east coast.
Authorities released video showing South Korean F-15K fighter jets firing air-to-ground missiles.
The weapons accurately hit their targets in the East Sea -- the Korean name for the Sea of Japan -- the South's Joint Chiefs of Staff said in a statement.
The exercise "was carried out as a strong warning" to the North for conducting its sixth nuclear test, it added.
The range to the simulated targets was equivalent to the distance to the North's Punggye-ri nuclear test site, where Sunday's test was conducted, it said.
North Korea on Sunday triggered global alarm with by far its most powerful atomic test to date, claiming it was a hydrogen bomb that could be mounted onto a long-range missile.
Following the test, South Korean President Moon Jae-In called for the "strongest punishment" while top military officers in Seoul and Washington vowed a joint "military counteraction" at the earliest date.
In a series of tweets posted hours after Sunday's test, US President Donald Trump denounced the North but also criticized Seoul.
South Korea, Trump said, "is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!"
Defense Secretary Jim also spoke out, saying "any threat to the United States or its territories, including Guam, or our allies will be met with a massive military response, a response both effective and overwhelming.
"We are not looking to the total annihilation of a country, namely North Korea," he added, but warned: "We have many options to do so."
Moon and Japanese Prime Minister Shinzo Abe agreed on Monday to pursue stronger United Nations sanctions against North Korea.
"Both heads of state agreed to cooperate closely with each other and the United States and shared the understanding there must be the most powerful sanctions and pressure applied on North Korea," presidential Blue House spokesman Park Su-hyun told a media briefing.
"And as part of that they agreed to push for more powerful UN sanctions," Park said after Moon and Abe spoke for about 20 minutes by phone. The aim of stronger sanctions was to draw North Korea into dialogue, he said.