Ever heard of the Khorasan Group?

You might want to bone up on it.

WASHINGTON (AP) — While the Islamic State group is getting the most attention now, another band of extremists in Syria — a mix of hardened jihadis from Afghanistan, Yemen, Syria and Europe — poses a more direct and imminent threat to the United States, working with Yemeni bomb-makers to target U.S. aviation, American officials say.

At the center is a cell known as the Khorasan group, a cadre of veteran al-Qaida fighters from Afghanistan and Pakistan who traveled to Syria to link up with the al-Qaida affiliate there, the Nusra Front.

But the Khorasan militants did not go to Syria principally to fight the government of President Bashar Assad, U.S. officials say. Instead, they were sent by al-Qaida leader Ayman al-Zawahiri to recruit Europeans and Americans whose passports allow them to board a U.S.-bound airliner with less scrutiny from security officials.

In addition, according to classified U.S. intelligence assessments, the Khorasan militants have been working with bomb-makers from al-Qaida's Yemen affiliate to test new ways to slip explosives past airport security. The fear is that the Khorasan militants will provide these sophisticated explosives to their Western recruits who could sneak them onto U.S.-bound flights.

It's called war, and they're waging one on us.