Washington (CNN) Despite the collapse of its territorial caliphate, ISIS remained a growing and evolving threat even as it lost territory in Syria, a top State Department official said Friday.

Counterterrorism Coordinator Ambassador Nathan Sales, speaking just days after the death of ISIS leader Abu Bakr al-Baghdadi, said the terrorist organization spread its influence through affiliates and individual actors.

"Terrorist fighters are always looking for the next battleground," Sales told reporters during a briefing to unveil the department's 2018 Country Reports on Terrorism . "And I think we're concerned about the possibility that jihadis who've been defeated in Syria might relocate elsewhere, whether you're talking about ISIS Khorasan in Afghanistan or moving into the Sahel ."

President Donald Trump claimed the defeat of ISIS in Syria in December 2018 as justification for his hasty decision to remove US troops from that country -- a decision that he walked back and reinstituted in various iterations, including in the past several weeks. Gen. Mazloum Abdi, the commander of the US-allied Syrian Democratic Forces, announced in late March that the physical caliphate had been defeated. Trump has repeatedly touted his role in the group's territorial defeat. However, the State Department report noted that in 2018, ISIS "proved its ability to adapt, especially through its efforts to inspire or direct followers online."

"As the false caliphate collapsed, we saw ISIS' toxic ideology continue to spread around the globe in 2018," Sales told reporters Friday. "ISIS recognized new regional affiliates in Somalia and in East Asia. Foreign terrorist fighters headed home or traveled to third countries to join ISIS branches there. And homegrown terrorists, people who have never set foot in Syria or Iraq, also carried out attacks."

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