Obama's foreign policy has come under fire as it was revealed that the US dropped 1,600 bombs in Syria and Iraq last month alone at a cost of $8.5m (£5.6m) a day, according to the Times newspaper.

Since August 2014, 11,550 bombs have been dropped in those two countries, mostly by the US, which is leading air strikes against Islamic State (ISIS) in those countries.

Targets damaged or destroyed as of March include 75 tanks, 285 Humvees, 1,689 buildings, 1,166 fighting positions, 150 oil infrastructure sites, and 441 IS staging areas, according to the US Air Force.

Although Obama has been reluctant to deploy ground troops, more than 13,000 US military personnel are serving in war zones – 9,800 in Afghanistan, 3,100 in Iraq and now 300 training with Ukrainian government forces facing Moscow-backed rebels – the Times reported.

The military personnel on the ground have a non-combat mandate and are there to train and advise.

Obama foreign policy criticised

Obama swept to power in 2008 promising to end US involvement in ground conflicts in Afghanistan and Iraq.

He has largely achieved this goal, but his policy of only fighting conflicts using air power is being challenged by a number of critics.

They argue that Obama's foreign policy approach has been undermined and exploited by leaders hostile to America's interests.

One vocal critic is General Jack Keane, former vice-chief of the US Army.

"In every case, Obama has done something that's less than sufficient to be consequential.

"This is indisputable in Iraq, where there are not enough resources for the [Iraqi] ground forces to make them effective," he said.

Republican candidates have accused Obama of overseeing a decline in US influence on the world stage.

Senator Ted Cruz, who is fighting to be the republican candidate in the 2016 elections, said: "Today, the consequences of the Obama-Clinton foreign policy is [sic] that our friends no longer trust us, and our enemies no longer fear us."

Governor Rick Perry, another presidential candidate, said: "Our allies doubt us, and our adversaries are all too willing to test us."

Drones unpopular

His strategy has also been criticised by those protesting against drone strikes.

The announcement that a US drone attack killed two western hostages captured by Al-Qaeda in Afghanistan in January reignited the debate over the legitimacy of using airstrikes – especially drone strikes – to combat militants.

However, supporters of Obama's doctrine point to the progress made in negotiations over Iran's nuclear programme which saw an agreement on the framework of a deal agreed upon this month, with a final deal due by June 30.

A recent global poll assessing the leadership of the US, China, the European Union, Germany and Russia suggests Obama's foreign policy is popular around the globe, despite the unpopularity of the US drone programme, Bloomberg reported.