At a Kurdish-run refugee camp in Iraq, strict checks are being imposed to weed out "good" Sunni Arab families from "bad" ones suspected of links to the Islamic State group.

Families arriving at the northern camp of Aliama without men are forced to explain their absence and prove they are not jihadist fighters, even by providing certificates if they are no longer alive.

Kurdish officials are desperate to avoid taking any chances, especially after a bomb attack on a convoy of Kurdish peshmerga forces killed four of them.

"We know that refugees did that," says General Halgord Mulla Ali, a peshmerga spokesman in the autonomous Iraqi region of Kurdistan, without elaborating.

Jihadist fighters from the Sunni-led Islamic State group launched an offensive on Iraq on June 9 and soon took over much of the country's Sunni heartland, after capturing chunks of eastern Syria.

Their advance has sparked an exodus of refugees, including hundreds of wives and children of IS jihadist fighters, into Kurdistan.

"Here 99 percent of the families are Sunni Arabs," says Taleb al-Dalawi, who runs the Aliama camp on the outskirts of the city of Khanaqin, northeast of Baghdad and close to the border with Iran.

The refugee centre is home to 1,745 families, including 150 unaccompanied by husbands or fathers.

In order to gain access, the refugees must provide camp officials with the Iraqi "family book" -- a government-issued document that serves as an identity card listing the names of the spouses and those of their children.

"If a woman arrives without a husband, we ask her to give us proof of where he is located, and if she claims he is dead we demand a death certificate," says Dalawi.

The Kurdish authorities leave no stones unturned as they investigate the men, engaging security services from across various regions.

Women found to have provided unsatisfactory details on the whereabouts of their husbands are thrown out of the camp, and usually end up squatting at construction sites.

But many choose to quit the camp -- also known as Ayden -- by themselves to avoid having to make excuses under the relentless questioning.

According to Dalawi, this happens when "the husband orders his wife to immediately leave the camp".

- Searching for weapons -

Currently, there are around one million Arabs displaced in Kurdistan, according to the peshmerga.

"Among them there are, obviously, good people. But there are also some who cooperate with the Islamic State," says Mulla Ali.

Iraqi government forces folded when the IS jihadists swept across five provinces, prompting the peshmerga to go on the offensive, backed by US-led air strikes and international weapons shipments.

While the peshmerga engaged the IS in deadly fighting on several fronts, Kurdish authorities have built their own defences.

Determined not to leave anything to chance, they also carry out searches of refugee tents in addition to the strict identity checks they run on them when they first arrive.

The searches are conducted by the asayesh, a Kurdish intelligence security outfit, and are meant to ensure the refugees are not hiding any weapons or explosives.

According to peshmerga Colonel Ali Abdullah, some searches have proven positive and weapons were found hidden by women whose husbands are IS members.

Security is also very tight in an annex of the Aliama camp, home to 150 families who have fled sectors of the province of Diyala overrun by the jihadists.

Families who arrived without a husband were turned away.

"If the man is not with his family and he is not dead, that can only mean that he is fighting in IS ranks," says Souar Ismail Hussein, who runs the annex.