Hillary Rodham Clinton has formally resigned as the 67th United States secretary of state, capping a four-year tenure in the office that saw her travel extensively across the world as the country's top diplomat.
In a letter sent to President Barack Obama on Friday shortly before she was to leave the State Department for the last time in her official capacity, Clinton thanked the president for the opportunity to serve in his administration.
Clinton said it had been an honour to be part of his cabinet and that she remained convinced of the "strength and staying power" of the US' global leadership.
"I am more convinced than ever in the strength and staying power of America's global leadership and our capacity to be a force for good in the world," she said in the letter.
Clinton shattered records for the number of countries visited by a US secretary of state. The former First Lady, once considered a divisive figure in American politics, leaves office as one of its most popular. But she remained coy about whether she would run for president in 2016.
"I am making no decisions, but I would never give that advice to someone that I wouldn't take myself," she said in an interview with The Associated Press on Thursday.
"If you believe you can make a difference, not just in politics, in public service, in advocacy around all these important issues, then you have to be prepared to accept that you are not going to get 100 percent approval."
Her resignation became effective at 4pm local time on Friday, when Supreme Court Justice Elena Kagan swore in John Kerry as the new top US diplomat. The former senator and 2004 Democratic presidential candidate is the 68th secretary of
"I'm just very, very honored to be sworn in and I'm very anxious to get to work," Kerry told reporters after the private ceremony at the Capitol. "I'll be reporting Monday morning at nine o'clock to do my part," he said, but refused to say what global hotspot he would visit first.