South Korea’s military conducted a major drill on Monday in response to the North’s claims on Sunday to have successfully conducted a hydrogen bomb test. South Korea’s army and air force conducted drills involving long-range air-to-surface missiles to “strongly warn” Pyongyang, Fox News quoted officials. South Korea added that more drills were being prepared with the United States’ forces in the country.

The South Korean military said it has seen indications that Pyongyang is preparing more missile launches, possibly even an intercontinental ballistic missile, The Guardian reported, citing local media. So, to counter these threats, it may temporarily install four missile defence launchers of the United States’ Terminal High Altitude Area Defence, or the Thaad, system. China, however, opposes this as its strong radar can possibly undermine Beijing’s security system.

The South Korean Defence Ministry also measured the North’s nuclear test on Sunday at 50 kilotonnes, and said that it was the strongest ever from Pyongyang.

United States Secretary of Defense James Mattis said the country will launch a “massive military response” to threats from North Korea, The Guardian reported. “We are not looking to the total annihilation of a country, namely North Korea,” Mattis said. “But we have many options to do so”.

While maintaining that the United States’ response will be effective and overwhelming, Mattis said it is clear that Washington has the ability to defend itself and allies South Korea and Japan. He also told North Korea’s leader Kim Jong Un to “de-nuclearise the Korean peninsula”.

The United Nations Security Council was set to meet on Monday to decide on fresh sanctions against North Korea, Mattis added. United States President Donald Trump had also said that the country was “considering stopping all trade with any country doing business with North Korea.”

Earlier, while asked if the US was planning to attack North Korea, Trump had said, “we will see”. Trump had also condemned North Korea for conducting a nuclear test that was “very hostile and dangerous to the United States”. “North Korea is a rogue nation, which has become a great threat and embarrassment to China, which is trying to help but with little success,” he had said.

India and other countries on Sunday had urged North Korea to refrain from actions that “adversely impact peace and stability in the region and beyond”

This was North Korea’s sixth underground nuclear test since 2006. It triggered an earthquake of magnitude 6.3 on Sunday morning. This quake was five to six times more powerful than the seismic activity recorded after Pyongyang’s fifth nuclear test. On Saturday, North Korea had claimed it had developed an “advanced hydrogen bomb” with “great destructive power”.