More than 60 people have been after returning to the UK from on suspicion of fighting alongside IsisYouTube

Isis (now known as the Islamic State) is plotting to smuggle its fighters into Western Europe disguised as Middle Eastern refugees, according to US intelligence sources.

German newspaper Bild reported that American intelligence authorities had unravelled encrypted talks between the leadership of IS.

The sources told the outlet IS was moving away from plans to conduct aircraft hijackings and attacks for fear of tight security and was looking to land a new strategy.

It is seeking to move militants across borders disguised as refugees in a "trojan horse" tactic that would see the fighters use fake passports once in Turkey to reach Western European countries in the hope of carrying out terror attacks.

"In view of the chaotic conditions on the Syria-Turkey border, it is nearly impossible to catch Isis terrorists in the wave of refugees," wrote Bild.

The porous nature of the Syrian-Turkish border has seen thousands of refugees from the Syrian civil war cross into the Nato member's territory.

The lax border controls allow IS militants to merge with genuine refugees seeking safety away from the war-weary country.

The discovery by US intelligence comes as the Syrian border city of Kobani continues to to bear the brunt of an IS offensive.

IS has raised two flags over the city's eastern district and is in control of Mistenur, the strategic hill overlooking the town.

Hundreds of Kurds from the YPG (Syrian-Kurdish militia) have crossed the Syrian-Turkish border to fight the terror group and protect the city, according to the YPG spokesman Redur Xelil.

Since the IS offensive on the areas surrounding the city began, approximately 150,000 civilians - mainly Syrian Kurds - have fled across the border into Turkey.

There are fears IS will embark on another mass slaughter - as it did with the Yazidi Kurds in the Iraqi town of Sinjar - if it captures Kobani. Despite the mass exodus into Turkish territory, 100,000 people remain in the city.

Esmat al-Sheikh, head of the Kobani Defence Authority, said: "If they enter, it will be a graveyard for us and for them. We either win or die. We will resist to the end."