Syrians and Libyans fleeing to Europe are committing sin by exposing their children to atheism, drugs, alcohol and sexual permissiveness, according to a magazine published by Islamic State insurgents.

Hundreds of thousands of people have fled wars in the Middle East this year, often from areas seized or threatened by Islamic State militants. They have crossed the Mediterranean to Europe on flimsy boats that have sometimes capsized, killing hundreds, in one of the biggest waves of migration since World War Two.

Most of the refugees come from Syria, Iraq and Libya – states ravaged by conflict frequently involving Islamic State.

"Sadly, some Syrians and Libyans are willing to risk the lives and souls of...their children, sacrificing many of them during the dangerous trip to the lands of the war-waging crusaders ruled by the laws of atheism and indecency," Islamic State's Dabiq magazine said.

It said that most families fleeing to Europe come from areas under Syrian President Bashar al-Assad's control or from Kurdish areas that had been fighting Islamic State.

But the magazine of Islamic State, which controls territory in Iraq and Syria where some 10 million people live, said those who leave its domain were committing a "major sin".

"It should be known that voluntarily leaving Dārul-Islām [lands of Islam] for dārul-kufr [land of unbelievers] is a dangerous major sin, as it is a passage towards kufr [disbelief[ and a gate towards one's children and grandchildren abandoning Islam for Christianity, atheism, or liberalism," it said.

Dabiq magazine added that migrating to Christian lands exposed children or grandchildren to "the constant threat of fornication, sodomy, drugs, and alcohol".

"If they don't fall into sin, they will forget the language of the Koran – Arabic – which they were surrounded by in Syria, Iraq, Libya, and elsewhere, making the return to the religion and its teachings more difficult."