South Korea's Yoon names new defence minister after botched martial law

South Korean President Yoon Suk Yeol has accepted the resignation of Defence Minister Kim Yong-hyun and nominated the ambassador to Saudi Arabia, Choi Byung-hyuk, as new defence minister, the presidential office said on Thursday.

Kim, who offered his resignation on Wednesday, was seen as a central figure in Yoon's declaration of martial law on Tuesday. A senior military official and filings to impeach Yoon by opposition members said Kim made the recommendation to Yoon.

The nomination is the first official move by Yoon after he announced the withdrawal of the martial law declaration in the early hours of Wednesday, amid a storm of political turmoil and diplomatic fallout. 

Parliament introduced a motion early on Thursday to impeach him over the botched attempt to impose martial law, but his party vowed to oppose the move, throwing the process into doubt.

The main opposition Democratic Party has called Yoon's martial law attempt a treasonous act, and its lawmakers could lead a vote for the bill as early as Friday.

US officials said they were caught completely off guard by Yoon's martial law declaration, which Deputy Secretary of State Kurt Campbell said was "badly misjudged".