The US Senate has unanimously passed a sweeping $631 billion Defence Bill, which issues new sanctions against Iran, changes the detention policy of American citizens and seeks quick action for withdrawal of this country’s combat troops from Afghanistan.

The Defence Authorisation Bill — passed by 98-0 votes by the Senate yesterday — would require the Chairman of the US Joint Chiefs of Staff to submit to Congress an assessment of the risk to the US mission and security interests associated with a reduction of American forces in Afghanistan.

“It is only the second time in 50 years there has been a unanimous vote on a Defence Authorisation Bill,” Senator Carl Levin, Chairman of the Senate Armed Services Committee, said.

“This Bill will enable our Armed Forces to continue to take the battle to al-Qaeda and other terrorist groups. Just as importantly, it keeps Democrats’ promises by supporting President (Barack) Obama’s plan to bring our troops home from Afghanistan,” Senate Majority Leader Harry Reid said after the passage of the Bill.

In view of the attack on the US Consulate in Benghazi, the Defence spending Bill also authorises an increase of up to 1,000 additional Marine Corps personnel assigned to the Marine Corps Embassy Security Group.

“It also provides the resources, training, equipment and authorities necessary for our military to succeed in Afghanistan and provides continued support to the Afghanistan National Security Forces as they assume increased responsibility throughout Afghanistan,” Senator John McCain said.

The House of Representatives has already passed the Defence Authorisation Bill.

Since there are differences on the two versions of the Bill, it now goes to the House-Senate conference committee, which needs to sort out the differences.

The Bill would provide $526 billion for the base defence Budget, $17 billion for Defence programmes in the Energy Department and $88 billion for the war in Afghanistan.

It also added new sanctions on Iran’s energy and shipping sectors in a fresh bid to scuttle its nuclear ambitions.

The White House has threatened to veto the Bill, if a series of measures, including restrictions on detainee transfers to foreign countries in the House version of the Bill, make it to the final Bill.