John Kerry hailed the contribution of outgoing Secretary of State Hillary Clinton at his official swearing in ceremony in Washington.
"I want to thank Secretary Clinton for the unbelievably high standard of energy, commitment and vision that she set in her superb stewardship of the US State Department," said Kerry.
The new Secretary of State also paid tribute to Barack Obama, saying: "The President has restored American's place and our reputation in the world."
More top news
Former Girls Aloud singer Kimberley Walsh is pregnant with her second child, she has revealed.
Chancellor George Osborne will seek to reassure financial markets on Monday morning following Britain's decision to leave the EU.
In his first outing since the referendum result, the lead Leave campaigner has outlined his vision for a post-Brexit Britain.