Islamic State fighters used a sandstorm that halted US airstrikes to seize critical military advantage in the terror group's attack on the provincial Iraqi capital of Ramadi, according to a media report.

The sandstorm delayed American warplanes and kept them from launching airstrikes to help the Iraqi forces, as the Islamic State fighters evidently anticipated, The New York Times reported.

The fighters used the time to carry out a series of car bombings followed by a wave of ground attacks in and around Ramadi, the capital of the Sunni heartland province of Anbar, that eventually overwhelmed the American-backed Iraqi forces.

Once the storm subsided, Islamic State and Iraqi forces were intermingled in heavy combat in many areas, making it difficult for allied pilots to distinguish friend or foe, US officials were quoted as saying by the daily.

By that point, the militants had gained an operational momentum that could not be reversed.

"The dust storm at the very least neutralised capabilities that could have been decisive," a former senior military official was quoted as saying.

The episode showed the limitations in America's formidable aerial arsenal and also the weaknesses in the Iraqi military's ability to reinforce and resupply troops facing heavy attack, particularly in Ramadi and elsewhere in Anbar Province, where the government has struggled to recruit capable Sunni troops, the report said.

Although American military officials challenged the notion last week that bad weather hindered the effectiveness of the airstrikes, other officials in the US and Iraq said on Monday that the sandstorms played a more important role than previously acknowledged.

Islamic State fighters have used this tactic before -- in January they launched a surprise attack against Kurdish forces in Kirkuk during a sandstorm -- but not with such formidable results.