The suspension of President Yoon Suk Yeol’s powers left a seasoned but unelected prime minister in charge of a country facing daunting challenges at home and abroad.

South Korea’s opposition leader offered Sunday to work with the government to ease the political tumult as officials sought to reassure allies and markets, a day after the opposition-controlled parliament voted to impeach conservative President Yoon Suk Yeol over a short-lived attempt to impose martial law.