The Islamic State of Iraq and the Levant (ISIL or ISIS) group is expanding its footprint in Afghanistan "with thousands and thousands" of fighters after losing its so-called caliphate in Syria and Iraq.
The armed group is recruiting new soldiers and plotting attacks on the United States and other Western countries, US and Afghan security officials say.
ISIL is seen as an even greater threat than the Taliban because of its increasingly sophisticated military capabilities and its strategy of targeting civilians, both in Afghanistan and abroad. Concerns run so deep that some officials have come to see the Taliban, which has also clashed with ISIL, as a potential partner in containing it.
A US intelligence official based in Afghanistan told The Associated Press a recent wave of attacks in the capital, Kabul, were "practice runs" for even bigger assaults in Europe and the US.
"This group is the most near-term threat to our homelands from Afghanistan," the official said on condition of anonymity, adding ISIL's "core mandate" was to conduct "external attacks".
"That is their goal. It's just a matter of time," he said. "It is very scary."