The West may have severely underestimated the strength of the Islamic State (IS) Sunni radical organisation, which may have raised an army of at least 200,000 fighters, a Kurdish leader has claimed.
This number is seven to eight times more than Western intelligence estimates of up to 31,500 fighters, said Fuad Hussein, the chief of staff of Kurdish President Massoud Barzani, in an exclusive interview to The Independent on Sunday.
Hussein speculates that the CIA and US intelligence agencies may only have been speaking about "core" fighters in estimating the jihadis' numbers.
He said that the ability of the IS to attack on many widely separated fronts in Iraq and Syria at the same time is proof of its swelling numbers.
"They are fighting in Kobani," said Hussein. "In Kurdistan last month, they conducted assaults in seven different places as well as in Ramadi (the capital of the Anbar province, west of Baghdad) and Jalawla (an Arab-Kurdish town close to the Iranian border). It is impossible to talk of 20,000 men or so."
He estimates that the IS rules a third each of Iraq and Syria, with a population of 10 to 12 million, living in an area of 250,000 sq km, the same size as Britain. This is held to give the jihadis a large pool of potential recruits.
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"I am talking about hundreds of thousands of fighters, because they are able to mobilise young Arab men in the territory that they have taken," Hussein was quoted as saying.
The huge numbers of the IS underlines that it will be difficult to eliminate it even with US airstrikes.
The underestimation of IS's size may explain why the US and other foreign governments have been repeatedly caught by surprise over the past five months, as the militants inflicted successive defeats on the Iraqi and Syrian armies, the Syrian rebels and the Kurdish Peshmerga.
The US and its allies are now beginning to take on board the obstacles to fulfilling President Obama's pledge to degrade and destroy the IS.
The chairman of the US Joint Chiefs of Staff, Gen. Martin Dempsey arrived in Baghdad Saturday "to get a sense from our side about how our contribution is going".
Earlier in the week, he told the US Congress that to defeat the IS, an efficient army of 80,000 men would be necessary. Few in Iraq believe that the country's regular army is up to the task.
The Kurdistan Regional Government now faces IS units along a 650-mile frontline cutting across northern Iraq, between Iran and Syria.
As well as terrifying its opponents by publicising its own atrocities, the IS had developed an effective cocktail of tactics that includes suicide bombers, mines, snipers and the use of US equipment captured from the Iraqi army such as Humvees, artillery and tanks.
To combat them, the Kurds need Apache helicopters and heavy weapons such as tanks and artillery, Hussein said.
The fighting over the past five months has shown that the IS has become a formidable military force, according to the Kurdish leader.
"We are talking about a state that has a military and ideological basis," said Hussein, "so that means they want everyone to learn how to use a rifle, but they also want everybody to have training in their ideology, in other words brainwashing."
A sign of IS's military professionalism is the speed with which they learned to use captured foreign weaponry.
"They will fight until death, and are dangerous because they are so well-trained and they have the best snipers," Hussein was quoted as saying.
There is supporting evidence for Hussein's high estimate of IS numbers. A study by the National Security Adviser's office in Baghdad before the IS offensive showed that when 100 jihadis entered a district, they would soon recruit between five and 10 times their original number.
There are reports of many young men volunteering to fight for the IS when they were in full flow, though this enthusiasm may have ebbed since the US started aerial strikes.
In an impoverished region with few jobs, the IS pay of $400 a month is also attractive.
Moreover, Hussein says that in the places that the IS have conquered, they are remodelling society in its own image, aiming to make people accept the IS ideology.
The IS, formerly called the Islamic State of Iraq and the Levant (ISIL), is a Sunni jihadi organisation and last June self-proclaimed a "caliphate" in areas it controls in Iraq and Syria. The group has been named a terrorist organisation by the UN and European Union (EU).
On June 29, it proclaimed the "caliphate" under its leader Abu Bakr al-Baghdadi and the group was renamed the Islamic State.