US President Barack Obama yesterday nominated Senator John Kerry as his new secretary of state, as he began to reshape his national security team for a second term clouded by increased global turmoil.

Kerry, 69, a decorated Vietnam War veteran, defeated former presidential candidate and experienced foreign policy hand, would succeed Hillary Clinton, who is stepping down after four years as the top US diplomat.

“Over these many years, John's earned the respect and confidence of leaders around the world,” Obama said at the White House as he announced Kerry's nomination, his first second-term cabinet pick.

“He is not going to need a lot of on the job-training.”

Kerry stepped up following the withdrawal of UN Ambassador Susan Rice, the early favourite for the post, who was caught in the political aftermath of the attack of the US Consulate in Benghazi, Libya in September.

Obama said that Kerry, chairman of the Senate Foreign Relations committee, had played a central role in every US foreign policy debate for 30 years and that his “entire life had prepared him for his new role”.

Obama said that Clinton had hoped to be at the announcement, but was still recovering from a serious virus and a concussion.

The White House had hoped to make a clean sweep by announcing all nominations to the national security team.