WASHINGTON - US President Barack Obama ignored warnings from senior military and intelligence officials that the fall of Syrian President Bashar al-Assad would lead to “chaos” and extremist militants taking over the war-torn country, according to a Pulitzer prize-winning American investigative journalist.

"Barack Obama's repeated insistence that Bashar al-Assad must leave office - and that there are 'moderate' rebel groups in Syria capable of defeating him - has in recent years provoked quiet dissent, and even overt opposition, among some of the most senior officers on the Pentagon's Joint Staff," Journalist Seymour Hersh writes in the London Review of Books. "Their criticism has focused on what they see as the administration's fixation on Assad's primary ally, Vladimir Putin. In their view, Obama is captive to Cold War thinking about Russia and China, and hasn't adjusted his stance on Syria to the fact both countries share Washington's anxiety about the spread of terrorism in and beyond Syria; like Washington, they believe that Islamic State must be stopped."

Hersh writes that a highly classified 2013 Defence Intelligence Agency/Joint Chiefs of Staff report on Syria forecast that the fall of the Assad regime would lead to "chaos" and possibly to Islamist extremists taking over Syria.

Hersh reports that Lieutenant General Michael Flynn, director of the DIA between 2012 and 2014, told him that his agency sent a "constant stream" of warnings to the "civilian leadership" about the dire consequences of ousting Syrian President Bashar al-Assad.

The DIA's reporting "got enormous pushback" from the Obama administration, Hersh quotes Flynn as saying. "I felt that they did not want to hear the truth."

The report, published in the Jan. 7, 2016 edition of the London Review of Books, relies heavily on an anonymous former senior adviser to the Joint Chiefs of Staff.

Hersh writes that the adviser told him the DIA/Joint Chiefs report took a "dim view" of the Obama administration's insistence on continuing to finance and arm the so-called moderate rebel groups and found that the covert US programme to arm and support those "moderate" rebels fighting Assad had been co-opted by Turkey, which then morphed the programme into an "across-the-board technical, arms and logistical program for all of the opposition, including Jabhat al-Nusra and Islamic State."

"The assessment was bleak: there was no viable 'moderate' opposition to Assad, and the US was arming extremists," Hersh wrote.

In October, the Pentagon announced that it was discontinuing its programme to train and equip moderate rebels in Syria, saying the programme cost $500 million and only succeeded in training a "handful" of recruits.

In November, however, the CIA increased its shipments of arms to rebels in Syria, joining with US allies in challenging Russia and Iran's involvement in Syria in support of the Assad regime.

US officials, according to a Nov. 4 article in The Wall Street Journal, said the Obama administration is pursuing a dual-track strategy in Syria, to keep military pressure on Assad while US diplomats "see if they can ease him from power through negotiations."

The White House has not responded directly to the allegations raised in the article in the London Review of Books.

Its author, Seymour Hersh, won a Pulitzer Prize in 1970 for his reporting on the My Lai Massacre during the Vietnam War and has continued to write on national security for many newspapers and magazines, including The New Yorker. He was widely criticized for his The Killing of Osama bin Laden report that accused President Barack Obama and his administration of lying about the circumstances surrounding the killing of Osama bin Laden in 2011. Many media establishments, intelligence analysts and officials, including the White House, rejected the claim.