US President Elect Barack Obama has now selected half of the members of his cabinet with the announcement yesterday that he had picked a national security team led by Hillary Clinton and Robert Gates.

The selection completed the top tier of the team that will advise Mr Obama on foreign and national security issues in an era marked by wars in Iraq and Afghanistan and terrorism around the globe.

The President Elect made the appointments at an unusually quick pace during his transition as he seeks to fulfil his goal of being able to "hit the ground running" when he takes the oath of office.

At a news conference in Chicago, Mr Obama introduced Mrs Clinton first, saying of his former presidential rival: "She possesses an extraordinary intelligence and toughness, and a remarkable work ethic.

"She is 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."

Mrs Clinton will give up her seat as a US senator to join the Obama cabinet as Secretary of State.

Her appointment was preceded by lengthy negotiations involving her husband, former president Bill Clinton, whose international business connections posed potential conflicts of interests.

Mr Clinton agreed to disclose the donors to the foundation that built his library, as well as contributors to his international foundation.

Mrs Clinton said to Mr Obama, in a brief turn at the lectern: "I am proud to join you and may God bless you and our great country."

The former first lady had scarcely finished speaking when her husband issued a statement, saying: "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."

Mr Gates, who served in George W Bush's administration, will be Defence Secretary.

He said 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," he said of the men and women in uniform in Iraq, Afghanistan and elsewhere. "How could I do otherwise?"

His presence in Chicago made him a visible symbol of the transition in power from the Bush administration to one headed by Mr Obama.

His appointment also fulfilled a campaign promise by Mr Obama to put a Republican in his cabinet.

Meanwhile, former Justice Department official Eric Holder was named Attorney General.

Mr Holder vowed to revitalise a Justice Department staggered by scandal during the Bush administration, both over the dismissal of federal prosecutors and the administration's programme of wiretapping as part of its war against terrorists.

Arizona governor Janet Napolitano was named Secretary of Homeland Security.

Like Mrs Clinton, Ms Napolitano must resign her current job. As a border state governor, she has experience with immigration issues, one of the pressing concerns that will confront the new administration.

Mr Obama also introduced retired marine general James Jones - a former top commander of Nato - as White House National Security Adviser.

The incoming president said Mr Jones will bring to the job "the dual experience of serving in uniform and as a diplomat".

"He has commanded a platoon in battle, served as supreme allied commander in a time of war and worked on behalf of peace in the Middle East," added Mr Obama.

Speaking following the announcement of Mrs Clinton's post, Britain's Foreign Secretary David Miliband said that he was looking forward to working with her on issues of common interest.

"Obviously Senator Clinton brings an enormous breadth of experience to her role," he said. "The quality that I would pick out is a determination to defy fatalism.

"She is someone who believes that human effort can engineer change and I think that that is a profoundly important quality."

Mr Obama takes office on January 20.

All the nominees are expected to win quick confirmation by the Democratic-controlled Senate.