Seoul, South Korea CNN  — 

South Korea’s military conducted a live-fire exercise early Monday in response to North Korea’s latest nuclear test.

The combined drill, carried out by the South Korean army and air force and intended to simulate a strike on North Korea’s nuclear test site, involved surface-to-surface ballistic missiles and F-15K fighter jets hitting targets off the east coast of South Korea, according to a statement form the country’s Joint Chiefs of Staff.

What happened:

– North Korea said it successfully conducted a test of a hydrogen bomb Sunday – the country’s sixth nuclear test.

– The explosion created a magnitude-6.3 tremor, making it the most powerful weapon Pyongyang has ever tested.

– Hours before the test, North Korean state media released pictures of the country’s leader, Kim Jong Un inspecting what it claimed was a nuclear warhead being placed inside a missile

Latest developments:

– US Treasury Secretary Steven Mnuchin said he is drafting tough sanctions against North Korea, adding “this isn’t the time for just talk.”

– As US President Donald Trump was leaving a church service for Hurricane Harvey victims, he was asked by a reporter if the United States would attack North Korea. “We’ll see,” Trump responded.

– US Defense Secretary James Mattis told reporters in front of the White House that any threat to the United States, its allies or its territories “will be met with a massive military response, a response both effective and overwhelming.” He added: “Kim Jong Un should take heed of the United Nations Security Council’s unified voice. All members unanimously agreed on the threat North Korea poses and they remain unanimous in their commitment to the denuclearization of the Korean Peninsula … We are not looking to the total annihilation of a country, namely North Korea, but as I said, we have many options to do so.”

Trump took to Twitter after the announcement and said North Korea’s “words and actions continue to be very hostile and dangerous to the United States.” He added that Pyongyang has become a “great threat and embarrassment to China, which is trying to help but with little success”; warned South Korea their “talk of appeasement with North Korea will not work”; and said Washington is considering “stopping all trade with any country doing business with North Korea.”

– Chinese President Xi Jinping, who is hosting an international financial summit, said in an opening ceremony speech that “incessant conflicts in some parts of the world and hotspot issues are posing challenges to world peace,” according to a transcript published by Chinese state media.

– Japanese Prime Minister said the threat against his country is now “more grave and imminent”; South Korean President Moon Jae-in called it an absurd strategic mistake.”

Emergency session

United Nations Secretary-General António Guterres said the test was “profoundly destabilizing for regional security,” and the UN Security Council has scheduled an emergency meeting to discuss the issue for Monday at 10 a.m. ET.