Director of National Intelligence Dan Coats told a Senate panel that homegrown terrorists pose "the most frequent and unpredictable terrorist threat to the United States homeland."
He said that while ISIS had lost territory in Iraq and Syria, the intelligence community has assessed its threat to the US continues due to its ability to both direct and inspire attacks. He added that ISIS was attempting to connect its global branches outside of Iraq and Syria more closely.
Beyond terrorism, Coats said that North Korea posed a "potentially existential threat" to the US, as North Korean leader Kim Jong Un continues to try to develop a nuclear weapon that could hit the US homeland.
Lt. Gen. Vincent Stewart, the head of the Defense Intelligence Agency, added that North Korea has not yet tested a long-range nuclear missile but is on the path to doing so.
"The interaction with the Chinese of late, I think, can play a significant role in terms of how we deal with this," Coats added.
Coats' assessment of the worldwide threats facing the US, delivered before a rare public hearing before the Senate intelligence committee, also predicted that the political and security situation in Afghanistan will "almost certainly deteriorate through 2018," even if there is a modest boost in military assistance from the US and other NATO allies.
President Donald Trump is currently weighing an increase of 3,000 to 5,000 US troops in Afghanistan in an effort to stabilize the fight against the Taliban and terror groups there.
Stewart described the situation in Afghanistan as a "stalemate," a characterization that dates back to the Obama administration. But he warned that "left unchecked, that stalemate will deteriorate in the favor of belligerence."
"We have to do something very different than we've been doing in the past," Stewart said. "They've got to get more trainers below the corps level ... or they have to get more personnel on the ground."
Coats also said that the Iraqi government would continue to face serious challenges to its stability and political viability, even as the threat from ISIS decreases as the effort to oust it from its major stronghold in the city of Mosul intensifies.
On Syria, Coats said the Syrian government was "both willing and able" to use chemical weapons in future attacks during the bloody civil war raging there, but he added that the intelligence community doesn't know if Damascus plans to do so.
He added that the intelligence community continues to investigate whether Russia had advance knowledge of Syria's alleged sarin attack against civilians on April 4.
And on the Iran deal, the director of national intelligence said the implementation of the nuclear deal struck by the Obama administration had extended the amount of time Iran would need to produce the fissile material for a nuclear weapon from a few months to about a year.