John Kerry succeeds Hilary Clinton

Hillary Rodham Clinton formally resigned on Friday as America's 67th secretary of state, ending a four-year tenure that saw her shatter records for the number of countries visited, as John Kerry was sworn in as the country’s new diplomatic leader.

In a letter sent to President Barack Obama shortly before left the State Department for the last time in her official capacity, Clinton thanked her former foe for the 2008 Democratic presidential nomination for the opportunity to serve in his administration. Clinton said it had been an honor to be part of his Cabinet.

'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.

Her resignation became effective on the swearing-in of her successor, John Kerry, who took take the oath of office in a private ceremony later Friday.

The former Massachusetts senator and 2004 presidential candidate was sworn in Friday by Supreme Court Justice Elena Kagan becoming the 68th secretary of state.

'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 9 o'clock to do my part.'

Kerry told The Boston Globe earlier on Friday that he was President Obama’s choice for secretary of state for some time, even as UN Ambassador Susan Rice came under heavy fire as a possible nominee for the position.

‘He called me, actually a week before Susan got out of the thing,’ said Kerry. ‘He called me and said, ‘You’re my choice. I want you to do this.’ He asked me to keep it quiet. I did. I sat on it.’

Kerry was sworn in at around 4pm EST on Friday as his predecessor’s resignation became official.

In the State Department's main lobby, Clinton pushed through a throng of American foreign service workers who clamored for handshakes and smartphone photos with her and gave an emotional goodbye speech.

She told them to continue to ‘serve the nation we all love, to understand the challenges, the threats and the opportunities that the United States faces and to work with all our heart and all of our might to make sure that America is secure, that our interests are promoted and our values are respected.’

Clinton, however, also left office with a slap at critics of the Obama administration's handling of the September attack on a U.S. diplomatic mission in Libya.