SEOUL, South Korea — South Korean President Yoon Suk Yeol vowed Thursday to “fight to the end” as he faces calls to step down over his failed attempt to impose martial law, defending his actions and lashing out at his political opponents in a defiant speech.

In a lengthy national address, Yoon accused “anti-state forces” in the opposition-controlled parliament of paralyzing the government and undermining the rule of law. He largely repeated comments he made last week when he…