On Thursday, Mr Moon attempted to assuage the concerns of South Koreans, saying Washington would not take military action without Seoul’s consent.
“The US and President Donald Trump too have agreed to discuss any options it may take with South Korea regardless of what kind of options it takes,“ he added.
He denied the two allies had conflicting approaches to dealing with North Korea, despite their different rhetoric.
Commenting on the South Korean president’s “red line“ remarks, Bong Youngshik, an expert on North Korea, said: “Mr Moon dug himself a deep hole. He made a strategic mistake.“
“He was way too specific. What if South Korea is pressed by Washington that North Korea has actually already crossed that red line? How can Seoul justify remarks about no military action on the peninsula?“
While failing to specify what the red line meant, the South Korean leader vowed that Pyongyang would endure more sanctions if it conducted further provocations.
The rhetoric underscores the fine line Mr Moon is attempting to walk of being tough but also diplomatic with Mr Kim.
Koh Yu-hwan, a professor of North Korean studies at Dongguk University, said that while Mr Moon would have felt public pressure to set a red line, he could now find himself boxed in.
首尔东国大学(Dongguk University)从事朝鲜研究的教授高有焕(Koh Yu-hwan)表示，虽然文在寅可能在公众压力下设定了一条红线，但现在他可能察觉到自己是作茧自缚。“
“Giving a red line to the North is practically setting a limitation on the [South Korean] president. There will be no room for negotiation or dialogue if the North passes it.“
Seoul — just 60km away from the 38th parallel that marks the frontier between the two Koreas and home to more than 20m people — stands to suffer the most from any North Korean retaliatory strikes emanating from a conflict between Washington and Pyongyang.