North Korea has ignored international condemnation and continued its efforts to push forward and create a deadly arsenal of nuclear weapons.
US President Donald Trump has used his tour of Asia to put more pressure on Kim Jong-un amid fears of the potential breakout of World War 3.
However, David Tafuri, an international lawyer, has suggested an aerial campaign against North Korea may not be sufficient to end its nuclear threat.
Mr Tafuri told Fox News: “The conundrum with North Korea is our normal ways for solving a problem with a foreign country, like diplomacy and sanctions, have not worked so far.
“That’s why we have to keep talking about military options. Now, the Joint Chiefs, just a couple of days ago, were talking about military options.
“And, they reminded people that even if we use a full-on air campaign, we probably can’t get all of North Korea’s nuclear weapons.
“That means we will have to invade. In the simplest terms, that means there will be a lot of collateral damage for us and also allies, like South Korea and Japan.”
Hours before the US President landed in South Korea, the North threatened “merciless retaliation” following Mr Trump’s comments in Japan.
Speaking in Tokyo, the US President said: “We are working to counter the dangerous aggressions of the regime in North Korea.
“The regime continues development of its unlawful weapons programs, including its illegal nuclear tests and outrageous launches of ballistic missiles directly over Japanese territory, are a threat to the civilised world and international peace and stability.
“We will not stand for that: the era of strategic patience is over.”
After arriving in South Korea, Mr Trump said he planned to talk about trade, as well as the North Korea crisis.
He said: “There is great cooperation.
“We have a terrific meeting scheduled on trade in a little while with President Moon and his representatives.
“And hopefully that will start working out and working out so that we create a lot of jobs in the United States which is one of the reasons that I’m here.”
They will also discuss how to maintain the 28,500 US troops stationed in South Korea, which is said to be a costly measure despite tensions with the North.