South Korea and the United States are "in communication at all levels" as needed, a foreign ministry official said Thursday, after a senior US diplomat's comment on South Korea's martial law turmoil drew attention for its critical tone.

US Deputy Secretary of State Kurt Campbell said Wednesday (US time) that President Yoon Suk Yeol "badly misjudged" when he declared martial law late Tuesday and ended it hours later following a parliamentary vote.

Speaking at a forum in Washington, Campbell also pointed out that the public reaction and the legislative procedures that ended the martial law were a manifestation of its people being prepared to stand up to "a deeply illegitimate process."

"Necessary communication is taking place between South Korea and the US at all levels," ministry spokesperson Lee Jae-woong said in a briefing, without elaborating when asked to comment on Campbell's remarks.

"The US has reaffirmed its ironclad commitment to our alliance," Lee said.

It is considered rare for a senior diplomat to use such an expression in reference to a decision made by the leader of an ally.

While South Korea reportedly did not inform the US of its plan to declare martial law in advance, the allies have been in talks over issues over the aftermath.

In a separate release later in the day, the ministry added that close communication between Seoul and Washington has been maintained at all levels following the martial law declaration.

"The government will strive to ensure the South Korea-US alliance continues to develop unwaveringly through constant communications," it said.