The Pentagon has given US President Donald Trump a secret plan to defeat the terror group IS, which is a little more than an "intensification" of what the Obama administration had, senior officials who reviewed the document told NBC News.

Trump had promised during the campaign to implement a "secret plan" to defeat the Islamic State, including a pledge to "bomb the hell out of" the terror group in Iraq and Syria.

However, the plan calls for continued bombing; beefing up support and assistance to local forces to retake its Iraqi stronghold Mosul and ultimately the IS capital of Raqqa in Syria; drying up IS's sources of income; and stabilising the areas retaken from IS, the officials said in an exclusive interaction with NBC News.

Two prominent military strategists told the television channel on Friday that they fear the plan is insufficient, and would not fulfil Trump's pledges to "totally obliterate IS" and do it quickly.

"The current plan to defeat the Islamic State is just like that old saying: Plan B is just, 'Try harder at Plan A,'" said retired Admiral James Stavridis, an NBC News analyst. 

"We have not come up with new ways of approaching this. I would say the President might want to send that report back to his team to take another hard look."

Retired Air Force Gen Dave Deptula, who planned the air campaign in the first Iraq war and is a vigorous advocate of conventional air power, insisted that the military should be directing more firepower at the IS.

Last week, the commander of US Central Command, Gen Joseph Votel, signalled to Congress that the current approach was working. 

"The Counter-IS campaign has entered its third year and we are on track with the military plan to defeat the terrorist organisation in Iraq and Syria," said Votel in testimony prepared for the Senate Armed Services Committee.

"If you view the Islamic State as a body, what's been going on with the current strategy is we've been attacking their fingers and their toes," said Deptula.

The bombing campaign against IS over the last two and half years, Deptula noted, has been commanded by Army generals. He says more air power is needed and that the Army should no longer be commanding the airstrikes against IS.

The NBC News report says the irony of the similarities between the Obama plan and the Trump plan is that as a candidate, Trump repeatedly called Obama's IS strategy a failure.

"We have to be unpredictable starting now. But they're going to be gone," he said in August 2016. "IS will be gone if I'm elected President. And they'll be gone quickly."

Pentagon spokesman Navy Captain Jeff Davis told NBC News that the Defence Department's preliminary plan sent to the White House is a grand strategy – which places even more emphasis on diplomacy, economics and information than it does on the military. 

It creates, he says, a framework for more tactical questions to be answered later.

The plan "draws upon the whole-of-government, better synchronising public diplomacy, cyber, information, financial, as well as military instruments of power, and it enhances our coordination across regions," he added.