US Secretary of State Hillary Clinton pauses as she bids farewell on her last day in office at the State Department in Washington, Feb 1, 2013. [Photo/Agencies]

WASHINGTON - Hillary Clinton on Friday formally stepped down as the 67th US Secretary of State, ending her four- year tenure as the country's chief diplomat.

"Thank you," Clinton said in her farewell remarks at the lobby of the State Department building. "Just standing here looking out at all of you, the people I have been honored to serve and lead and work with over the last four years, is an incredible experience."

Since taking office in January of 2009, Clinton has visited 112 countries and covered over 950,000 miles, which makes her one of the most-traveled secretaries of state in US history.

But her legacy has also been marred by the deadly September 11 attack on the US consulate in Benghazi, Libya last year, which killed US ambassador to Libya Christopher Stevens and three other Americans. The State Department has been under harsh criticism for its inadequate protection of the US mission.

In her remarks, Clinton admitted that the Americans are living in "complex and even dangerous times", citing the fresh attack on the US embassy in the Turkish capital of Ankara on Friday.

"I am very proud to have been secretary of state. I will miss you," she told the State Department staff. "On a personal basis, let me wish all of you the very best."

Finishing her remarks, Clinton stepped out of the lobby and left the State Department building in a dark-blue limousine.

Democratic Senator John Kerry has been sworn in as the new secretary of state in a private ceremony on Friday, shortly after Clinton left office. State Department will hold a welcoming ceremony for Kerry on Monday.