Barack Obama said today that he expects there to be conflict within his new security team after confirming Hillary Clinton as his choice for US Secretary of State.

The President-elect selected his former presidential rival as America’s most senior diplomat in a controversial move that is designed to unite the Democratic Party as well as to bring a wealth of international experience to the post.

Mr Obama said the team he had assembled was “uniquely suited” to address the issues of the 21st century.

He said that the appointment of Mrs Clinton was a sign of the seriousness of his approach to foreign policy, highlighting her experience and her familiarity with many world leaders.

“Hillary Clinton possesses an extraordinary intelligence and a remarkable work ethic. I’m proud she will be our next Secretary of State,” Mr Obama said.

“She’s an American of tremendous stature who will have my complete confidence, who knows many of the world’s leaders, who will command respect in every capital, and who will clearly have the ability to advance our interests around the world."

A week after making his economic appointments, Mr Obama unveiled his national security team today. Mrs Clinton was not the only high-profile appointee as Robert Gates was confirmed as the Defence Secretary, a position he has held under President Bush since 2006.

Mr Obama said that he expected strong opposing voices within the group but that ultimately he would be solely responsible for policy. “I’m a strong believer in strong personalities and strong opinions,” he said. “I did not go around checking people’s political registration.”

But, he added: “The buck stops with me."

Mrs Clinton, a New York Senator, said that she welcomed the opportunity to help shape the future of the United States at a time of war and terrorist attacks around the world. “America cannot solve these crises without the world and the world cannot solve them without America.”

“I believe that the best way to help serve my country is to join President-elect Obama,” she said. “Mr President-elect, I’m proud to join you in what will be a difficult and exciting adventure.”

“The American people have demanded not just a new direction at home, but a new effort to renew America’s standing in the world as a force for positive change.”

As the next Secretary of State stepped away from the podium where she had accepted the post, her husband had already released a statement.

Bill Clinton, the 41st US president, said: “She is the right person for the job of helping to restore America's image abroad, end the war in Iraq, advance peace and increase our security, by building a future for our children with more partners and fewer adversaries, one of shared responsibilities and opportunities.”

Speaking in London earlier today, Condoleezza Rice, the current Secretary of State, also welcomed the appointment of Mrs Clinton.

“I know that she will bring enormous energy and intellect and skill to the position,” she said, adding that Mrs Clinton had a “deep love for the United States of America."

“I am very fond of her. She has worked very hard on behalf of the country,” Mrs Rice said.

The President-elect today claimed that he had assembled a formidable team with a combination of military and legislative experience.

General James L. Jones, a retired marine and former commander of NATO and US forces in Europe, will be National Security Adviser while Susan Rice was appointed as the US ambassador to the UN.

Mr Obama named Eric Holder, a Washington lawyer, as Attorney General and Janet Napolitano, the Governor of Arizona, as Homeland Security Secretary.

The selection of Mr Gates to retain his post fulfilled Mr Obama’s campaign pledge to include a Republican in his cabinet.

The Defence Secretary said that he was “mindful that we are engaged in two wars and face other serious challenges at home and around the world.”

“I must do my duty as they do theirs,” Mr Gates said of the men and women in uniform in Iraq, Afghanistan and elsewhere. “How could I do otherwise?”

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