The brutal, Al Qaeda-linked group rebels invited into Syria to help topple President Bashir Assad has virtually taken over northern Syria, raising fears that its brand of indiscriminate terror could spill into neighboring Turkey, where some 300 U.S. soldiers are based to protect Turkish airspace from Syrian missile attacks.
ISIS -- whose name has been translated as "Greater Syria" -- joined the Free Syria Army's bid to oust Assad, but now seeks to turn the embattled nation into a building block in a radical Sunni Islamic empire, or caliphate, across the Middle East. The group has captured towns and swaths of territory along the border with Turkey.
According to a recent analysis from Stratfor, a Texas-based global intelligence organization, ISIS "has dispatched hundreds of fighters north toward Turkey in response to closure of certain border crossings." Turkey has a powerful military, but even so, can't welcome an enclave of radical jihadists on its border, say experts.
“Turkey could be a target for them [ISIS ]… Not in the immediate future, but maybe in the far future,” said Yossi Melman, a top Israeli security expert and co-author of "Spies Against Armageddon: Inside Israel’s Secret Wars."
Melman said Turkey’s prime minister, Recep Tayyip Erdogan, is not a "real Muslim" in the eyes of ISIS because he is a relatively moderate Islamic leader.
The ISIS has “gained a lot of knowledge and experience about Turkey,” cultivated ties and could form sleeper cells, added Melman. “If I were a Turkish official, I would say, there is room for concern,” he said.
The shocking anti-Western and anti-Christian ideology of ISIS led its jihadis to dismantle a cross on the top of a church in the city of al-Raqqa and replace it with the black flag of Al Qaeda. When ISIS seized the Syrian town of Jarabulus, it imposed a madrassa -- a strict Islamic school -- on a moderate Muslim pupil population. An Al Qaeda flag blankets the front of the school.
ISIS declared the town to be the "Emirate of Jarabulus" and swiftly clamped down on women, pressing them to fully cover their bodies with hijabs and their faces with veils.
The fanatical ISIS Islamists have outlawed tobacco and implemented public executions in the Syrian villages under their control. Humanitarian aid to the millions of displaced refugees within Syria has been made more difficult because ISIS declared that it will kidnap and kill aid workers who enter Syrian territory. It is unclear if the International Committee of the Red Cross workers abducted this week in northern Syria -- an ISIS stronghold -- were victims of the ISIS.
Just last month, ISIS defeated a pro-Western rebel group, Northern Storm, in the city of Azaz. The intense clashes prompted the Turkish government to shut a series of border crossings. The growing strength of ISIS -- and its insatiable drive to secure more territory -- could mean the jihadis are bent on confronting Turkey.
The Stratfor analysis stated that, "If the ISIS attempts to fight the Turkish Army along the border, it will incur heavy losses. However, the border is long and difficult to control."
The Turkish authorities apparently went on the offensive this month to prevent an ISIS jihadist spillover. Sky News reported that Turkey has begun to construct a 6-foot high (2 meters) wall along its frontier with Syria, "to stem border security and smuggling problems." According to Sky, a government official said, "We haven't had border security problems in Nusaybin so far, but in that area it's extremely easy for people to cross illegally. It's almost like there is no border."
For now, jihadists may be content to consolidate power inside Syria's borders, according to Aymenn Jawad al-Tamimi, the Shillman-Ginsburg Fellow at the U.S.-based Middle East Forum, told FoxNews.com,
"I do not foresee any ISIS clashes with Turkish forces in the near future. It is not in their interest to provoke such a clash and it would risk seeing the
loss of their current northern strongholds (most notably, Jarabulus and Azaz)," al-Tamimi told FoxNews.com.
Al-Tamimi noted that Ankara has not moved to stop the flow of foreign jihadis into Syria via Turkey, likely because it sees them as a useful proxy against the Kurdish PYD/PKK [separatists in Turkey], which it fears much more as a threat to Turkish hopes for what is essentially a 'divide-and-rule' policy towards the region's Kurds."
Turkey's southern border to Syria has become a lawless entry point for foreign jihadis. Last month, Abu Omar, who Al Qaeda freed from Iraq's Abu Ghraib prison in July, managed to make his way to the Turkish city of Gaziantep and hence into Syria. Abu Omar has wide latitude to move around in Gaziantep. At the same time, nearly 300 U.S. troops operate Patriot surface-to-air missile interceptions systems on a hill overlooking the Turkish city -- a mere 90-minute drive to Syria’s highly dangerous border.
Abu Omar recently stated that more radical Islamists are on their way to Syria.
"Everybody wants to go for jihad in Syria," he told Foreign Policy journal.
He confirmed that he joined ISIS to create an Islamic caliphate, a radical Islamic empire bent on limitless expansion.
"Syria and Iraq are the same struggle to us. Both governments in Iraq and Syria are run by unbelievers, so we will fight both. Syria is currently very weak and close to falling into the hands of the mujahedeen [Jihadis]," said Abu Omar.
Benjamin Weinthal reports on human rights in the Middle East and is a fellow at the Foundation for Defense of Democracies. Follow him on Twitter @BenWeinthal