Washington, May 23 (IANS): The Pentagon announced on Friday that Iraqi forces had broken through months-long siege of the Beiji oil refinery by the extremist group Islamic State (IS) and started resupplying previously beleaguered Iraqi forces within the facility.

"In the past 72 hours, we have seen the Iraqi security forces make steady, measured progress in regaining some of the areas to the Beiji oil refinery despite the significant (IS) resistance in the form of improvised explosive devices (IEDs), suicide vehicle borne IEDs, as well as heavy weapon and rocket fire attacks," Xinhua quoted Brig. General Thomas Weidley as saying in a statement.

IS fighters launched one of their fiercest attack on the refinery in April and have been laying siege to about 200 Iraqi security forces there ever since. The refinery, located about 200 kms north of Baghdad, has not been working since last June.

Fighting to reclaim the town of Beiji, home to the oil refinery, has long been deemed as one of the priorities by the US military.

However, as the city of Ramadi, a major Sunni town, fell to hands of IS fighters last week, which was seen as the most significant setback for Iraqi forces in almost a year, doubt was cast on the effectiveness of US anti-IS strategy that merely focuses on air raids and offering what critics say insufficient arms and training to local anti-IS forces.

"While there has been some progress and some success, looking at the strategy today, we know now that the conceptional plan is fundamentally flawed," said General Jack Keane, former vice chief of staff of the army, during his Senate Armed Service Committee hearing on Thursday.

Meanwhile, Republican Senator John McCain, an influential voice on the US national defence policy, described US President Barack Obama's declaration after the fall of Ramadi that the US wasn't losing the fight against IS "mind-boggling".

"The president's strategy is certainly not succeeding. It's abject failure," McCain told CNN on Friday. "This is a disaster."

In an interview with The Atlantic released on Thursday, Obama called the fall of Ramadi a "tactical setback" and said he did not think the US was losing the fight against IS.

"There's no doubt there was a tactical setback," Obama told the magazine, adding that Ramadi had been vulnerable because the Iraqi force there were "not Iraqi security forces that we have trained or reinforced".

"There's no doubt that in the Sunni areas, we're going to have to ramp up not just training, but also commitment, and we better get Sunni tribes more activated than they currently have been," Obama said.