WASHINGTON (NewsNation) — The United States was surprised by South Korean President Yoon Suk Yeol’s brief declaration of emergency martial law, a White House National Security Council spokesperson told NewsNation Tuesday.

“The Administration is in contact with the ROK government and is monitoring the situation closely as we work to learn more,” the spokesperson said, referring to the abbreviation for the Republic of Korea. “The U.S. was not notified in advance of this announcement.”

“We are seriously concerned by the developments we are seeing on the ground in the ROK,” they concluded.

Yoon’s actions were swiftly opposed by the South Korean legislature, which voted to defy the president and lift martial law.

Yoon ultimately backed down and reversed his earlier declaration.

President Joe Biden — who was in Angola Tuesday — was briefed on events as they unfolded in South Korea.

Vedant Patel, a U.S. State Department spokesman, said at a press briefing Tuesday that the U.S. “hopes the situation in South Korea will be “resolved peacefully and in accordance with the rule of law.”

Patel emphasized that the U.S. alliance with South Korea remained “ironclad.”

Yoon declared martial law Tuesday night local time, accusing the opposition party of sympathizing with North Korea and vowing to eliminate anti-state forces.

In his speech, Yoon said he wanted “to defend the free Republic of Korea from the threats of North Korean communist forces and to eradicate the shameless pro-North Korean anti-state forces that are plundering the freedom and happiness of our people and to protect the free constitutional order.”