Governments and rebel groups are making concerted efforts to regain key territory lost to the jihadist group, but ISIS remains a formidable enemy, according to the top U.S. intelligence chief.
"Unfortunately, despite all our progress against ISIL (ISIS) on the battlefield and in the financial realm, our efforts have not reduced the group's terrorism capability and global reach," CIA Director John Brennan recently told Congress.
Brennan noted that ISIS has lost "large stretches" of territory in Iraq and Syria, has experienced a reduction of finances, and has struggled to replenish its ranks as fewer foreign fighters have been traveling to those countries.
But ISIS still has about 18,000 to 22,000 fighters in Iraq and Syria, he said.
"We need to take away their safe haven," Brennan said, noting these areas provide the terror group with the ability to train operatives and generate revenue.
So what is the latest picture across the region?
In a symbolic victory, troops from the Iraqi Federal Police raised the national flag over the Falluja mayor's office Friday. The move came nearly four weeks after the start of a U.S.-backed offensive to liberate the city, the last major ISIS foothold in Iraq's Anbar province.
And almost a week later, Falluja's neighborhoods have been retaken and cleared of any ISIS presence, with only al-Jolan in the northeast -- about 10% to 15% of the city -- yet to be liberated, according to Brig. Gen. Yahya Rasool, spokesman for the Iraqi Joint Operations Command.
Units from Iraqi counterterrorism forces, federal police and Iraqi air force are conducting military operations in al-Jolan and will soon retake that neighborhood and declare the entire city recaptured, Rasool added.
But it's been a fierce campaign, with fighting taking place street by street. And bombs remain, even if most ISIS fighters have been driven from the city.
Many houses are booby-trapped, forcing Iraqi forces to move slowly and methodically to clear improvised explosive devices, or IEDs. "They don't leave any house without first rigging it with explosives," one counterterrorism member told CNN.
Despite the optimism from senior commanders, it may be some time before Falluja is safe -- and even longer before residents can move back to the rubble that was their home.
Almost 14,000 families (up to 84,000 individuals) may have left Falluja and surrounding areas alone since the government offensive to retake the city began May 23, according to the U.N. refugee agency
Both Syrian forces in the south, and U.S.-backed Kurds from the north, are zeroing in on Raqqa.
Raqqa is going to be a tougher nut to crack than Mosul, said retired Gen. David Petraeus, referring to the major Iraqi city across the border that ISIS has occupied since 2014.
Syria is "incomparably more complex" than anything he has "ever seen or studied," said Petraeus, who formerly led coalition forces in both Iraq and Afghanistan.
"There are so many different factions now. There are so many different sides to this."
The fight against ISIS here is complicated by the damage wrought by U.S. coalition and Russian airstrikes, which invariably take the very lives they are trying to protect.
On Tuesday, at least 34 civilians were killed in airstrikes on Raqqa, with dozens more injured, according to the London-based monitoring group Syrian Observatory for Human Rights.
And ISIS is "very much underground now" in places such as Mosul and Raqqa, Petraeus told
CNN national security analyst Peter Bergen.
"They are getting hammered when they pop their heads up; they get hammered if they get in a convoy."
Meanwhile, a U.S.-backed alliance of Kurdish and Arab militias has entered the city of Manbij, northwest of Raqqa, the Syrian Observatory for Human Rights told CNN on Thursday.
U.S. officials say Manbij is a strategic supply point and the main hub for ISIS between Raqqa and Turkey.
The coalition force, supported by airstrikes from U.S. warplanes, has encountered fierce resistance while advancing, the observatory said.
Beyond Iraq and Syria, Brennan said ISIS' growing presence in Libya presents another significant challenge.
"The branch in Libya is probably the most developed and the most dangerous," he said, echoing concerns by other security officials that Libya's proximity to Europe is a problem.
"We assess that it is trying to increase its influence in Africa and to plot attacks in the region and in Europe."
This month, Libyan forces loyal to the U.N.-backed unity government retook parts of the port city of Sirte from ISIS militants, gaining ground in the extremist group's most significant stronghold outside Syria and Iraq. The offensive lasted almost two weeks and left more than 100 fighters dead and about 400 others wounded.
However, Libyan forces have encountered fierce resistance since, including three suicide car bombings. One detonated near a field hospital
in Sirte, according to the media wing of Al-Bunyan al-Marsous, a military offensive led by Libyan forces from Misrata.
The Pentagon has acknowledged small teams of U.S. special operations forces are on the ground in Libya, establishing relationships with local forces battling ISIS.
Brennan told Congress that ISIS has about 5,000 to 8,000 fighters inside Libya.
In remarkably blunt testimony
, President Barack Obama's nominee to command U.S. forces in Africa said Tuesday that more ground troops were needed in Libya to fight ISIS and agreed the current strategy of not bombing the terror group's affiliate there "makes no sense."
When asked by Sen. John McCain whether the United States had a strategy for Libya, Marine Corps Lt. Gen. Thomas Waldhauser said he didn't know about one.
The United States has conducted airstrikes against ISIS in Libya, including one in February that killed more than 40 operatives of the terror group, but Washington has since held off on additional strikes.