As tensions escalate, South Korean President Moon Jae-in promised his citizens last week there "will be no war on the Korean Peninsula ever again."
Moon, who took office in May, announced on his 100th day in office that US and South Korean policies are aligned on North Korea.
US President Donald Trump assured South Korea he would consult with them before making any military decisions on North Korea, according to Moon.
Moon said North Korea's development of nuclear weapons technology was "nearing" a red line, which he described as "completing an ICBM and weaponizing it with a nuclear head."
North Korea claims it has successfully miniaturized a nuclear weapon. While some experts believe it may have the technology, others caution that even if it doesn't, North Korea should be taken at its word.
"If North Korea provokes again, it will face with much harsher sanction and won't stand it in the end. I want to warn North Korea to do no more dangerous gambling," Moon said.
His comments about averting war echoed similar statements he made Tuesday that only South Korea could give consent to initiate any conflict with the North.
"The government, putting everything on the line, will block war by all means," Moon said.
China has also urged both Washington and Pyongyang to tone down the rhetoric and stop actions that inflame tensions, missile testing on North Korea's side and military exercises on the US and South Korean side.
China's Global Times newspaper, a state-run tabloid, was scathing of South Korea's decision to proceed with the drills.
"The drill will definitely provoke Pyongyang more, and Pyongyang is expected to make a more radical response," it said in an editorial.
"If South Korea really wants no war on the Korean Peninsula, it should try to stop this military exercise."