John Kerry, the veteran American politician and 2004 presidential candidate, has been sworn in as the United States secretary of state, replacing Hillary Clinton.

"I was very honoured to be sworn in and very anxious to get to work," Kerry told media with his wife, Teresa Heinz Kerry, by his side, after being sworn in by the Supreme Court Justice Elena Kagan.

"So I will be reporting Monday morning at 9 o'clock," he told the awaiting media at the Capitol on Friday. Besides his wife, he was joined by daughter Vanessa, brother Cameron, and his Senate staff, who presented him with a gift: the seat he say during his 28 years of service in the Senate.