The United States was not aware of South Korean President Yoon Suk Yeol's intention to declare martial law, U.S. Secretary State Antony Blinken told Reuters on Wednesday, adding that he was anticipating speaking with his South Korean counterpart in the coming days.

Yoon declared martial law in South Korea on Tuesday, before rescinding the decision hours later after a chaotic standoff between parliament and the army.

Speaking in an interview with Reuters in Brussels on the sidelines of a meeting of NATO foreign ministers, the top U.S. diplomat said it was vital that the process from now on play out peacefully and according to the rule of law.

"South Korean democracy is one of the most powerful stories anywhere in the world. It's very important that any disputes, differences, political differences, be resolved peacefully and pursuant to the rule of law. That's what we're seeing now. That's what's so important to sustain," Blinken said.

Washington had not been informed about the South Korean decision beforehand, he said.

"That's correct, we were not aware," Blinken said.