WASHINGTON -- Hillary Clinton has formally resigned from her post as U.S. secretary of state, capping a four-year tenure that saw her visit a record 112 countries.
In a letter quoted by the Associated Press, she thanked U.S. President Barack Obama for the opportunity to serve as Washington's top diplomat.
She wrote that she remains convinced of the "strength and staying power" of American global leadership.
State Department staff gathered in a farewell ceremony for Clinton, at which she told them, "I hope that you will continue to make yourselves, make me, and make our country proud."
Clinton's resignation becomes effective on the swearing-in of her successor, Senator John Kerry.
He is scheduled to take the oath of office in a private ceremony later on February 1.