The locals even have a nickname for the area, “Tora Bora”, after the mountain hideout al Qaeda leader Osama bin Laden fled to after the United States invaded Afghanistan in 2001, a senior Iraqi security official in the border region said.

In late January, three Revolutionary Guards were killed in the Bamo region fighting 21 Islamic State militants who had sneaked in from Iraq. Three militants detonated suicide vests and two others were killed in the clash, the Guards said.

Days earlier, Iran’s intelligence ministry found a weapons cache in the town of Marivan on the Iranian side of the border that included TNT, C4, electronic detonators, grenades, ammunition clips for AK-47 machine guns and rocket propelled grenades.

The clash and discovery indicate that Islamic State still has the ability to penetrate the tightly controlled security net of the Islamic Republic, which has largely managed to avoid the devastation wrought by the group in neighboring countries.

“Today (Islamic State) does not control a country ... in order to assert that they exist, they may carry out an attack any day,” Hossein Dehghan, a former defense minister and now an adviser to Supreme Leader Ayatollah Ali Khamenei, said in a recent interview with the semi-official Tasnim news agency.

Halabja, the largest town on the Iraqi side, is most often remembered for a chemical attack ordered by then-President Saddam Hussein in 1988 which left thousands dead.

The presence of religious militants in the area around the town is not new: at the city’s entrance hang portraits of Iraqi Kurdish security forces, known as Peshmerga, killed in the battle against Islamic State.

Prior to the U.S.-led invasion of Iraq in 2003, Abu Musab al-Zarqawi, the jihadist largely blamed for stoking a civil war between Iraq’s Sunnis and Shi’ites, led a group in the area called Ansar al-Islam, which merged with Islamic State in 2014.

Many of the Iranian and Iraqi Kurds now fighting with Islamic State are part of a second generation of militants largely influenced by Zarqawi’s deadly legacy, Iraqi security officials and Peshmerga commanders familiar with the matter say.

Sunni IS militants see Shi’ites, who make up the majority of Iran’s population, as apostates and have repeatedly threatened to carry out attacks in the Islamic Republic. Kurds make up about ten percent of Iranians and are predominantly Sunni.

Hamai Hama Seid, a senior Peshmerga commander and member of the Iraqi Patriotic Union of Kurdistan (PUK) party, said Kurdish IS militants take advantage of their knowledge of the language and region as well as strong cross-border ties.

“There are definitely ties between the Iranian and Iraqi extremists on the two sides of the border,” Seid told Reuters in the Iraqi border village of Tawila, only a few hundred meters from the Iranian border. He added:

“The militants exploited this area because it’s mountainous, difficult and wooded.”

Many of the young men are poorly educated and have few economic opportunities, allowing extremist recruiters to flourish, Iraqi security officials and Peshmerga commanders say.

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