Washington, US: As US Congress begins debate on authorising a new war, senators voted Thursday to install Ashton Carter as the new secretary of defence, making him the top civilian official overseeing the fight against the Islamic State while also trying to grapple with Iran, Russia and other hotspots amid tight Pentagon budgets.

Republicans said they hoped Carter, who has previously served as the No. 2 civilian at the Pentagon, would be an independent voice willing to push President Obama beyond his reticent approach — and the early going suggests they are right.

During his confirmation hearing last week he said he would consider revising the US military commitment in Afghanistan, and he broke with the White House in saying he believed the US should supply lethal arms to Ukraine, which is battling Russian-backed separatists.

Carter was easily confirmed on a 93-5 vote, marking the first Cabinet position to be filled by the new GOP-run Senate.

‘America needs a strong secretary of defence now more than ever,’ said Senator John McCain, chairman of the Armed Services Committee. ‘I think Dr. Carter will be a good secretary of defence.’

Still, McCain said Carter could have a tough time in the Obama administration, predicting that the president will hamstring him and keep most key decisions at the White House.