WASHINGTON — U.S. military advisers in Mosul have begun wearing black uniforms similar to those preferred by Iraq's most elite troops, an attempt by the Americans to blend in as they move about the front lines in what's become an arduous block-by-block fight with Islamic State fighters who remain entrenched there.

Multiple images of black-clad troops have been shared on social media in recent weeks. And while it's common for U.S. special operations personnel to wear their partners' military uniforms, this development is unique.

In Mosul, where the Iraqi-led campaign has worn on for five months, it demonstrates just how close to the action some Americans have moved since President Trump challenged the Pentagon to bring more force to bear on ISIS. At the same time, it highlights seldom discussed tactics used by Navy SEALs and other clandestine units at the forefront of the war on terrorism.

Video: Why U.S. troops in Mosul are wearing Iraqi uniforms

Video: Why U.S. troops in Mosul are wearing Iraqi uniforms

U.S. officials in Baghdad told Military Times that individual unit commanders determine what uniforms are appropriate for specific missions, and that there is no overarching policy dictating what gear can be worn on the battlefields of Iraq and Syria. Coalition forces, the officials said, abide by longstanding law-of-war regulations that stipulate military personnel must distinguish themselves from civilians.

Typically, that's done using uniform insignia, identifiable from a distance as outlined by the 1949 Geneva Conventions, said Jeffrey Addicott, who heads the Center for Terrorism Law at St. Mary's University in San Antonio, Texas. Before retiring from the Army, he was the senior legal adviser for all of its special forces units. But over the last 15 years, he noted, the lines have blurred. Many of America's adversaries — ISIS especially — don't ascribe to the same standards for war fighting, and the U.S. has adapted accordingly.

"In modern warfare," Addicott said, "our uniforms have subdued identification so as to protect our soldiers from enemy attack. They can cover and conceal better."

It would appear that's what's happening in Mosul. In one of the images shared on Twitterthis month, an unidentified U.S. service member is seen at the trigger of a MK13 sniper rifle, scanning for targets off in the distance. Beneath his body armor, he wears a long-sleeve black blouse like those issued by the Iraqi Counter Terror Service, which has taken a lead role in the effort to liberate Mosul. The operator's vest and helmet bear two brightly colored American flag patches.

In another photo, an unidentified dog handler is seen waving at a group of children as dozens of Iraqis mill about in a rubble-strewn city street. A third tweetshows what appears to be an American service member with his arm around the shoulder of an Iraqi operative. Though their weapons and protective gear are unique, the men's attire is indistinguishable except for a subtle striped camouflage pattern embedded within the westerner's uniform.

When U.S. troops remove their identifying markers, Addicott said, they risk losing their protected status as lawful enemy combatants. That's usually a big deal if Americans get captured. But with ISIS, he said, it probably wouldn't matter. "You're dealing with an enemy that's torturing and beheading people," he told Military Times. "They're going to kill you whether you're wearing a uniform or not."

There are several reasons — ranging from political to practical — why special operators are disguising themselves in Mosul, said Clint Emerson, a retired Navy SEAL and author of "100 Deadly Skills: The SEAL Operative’s Guide to Eluding Pursuers, Evading Capture, and Surviving Any Dangerous Situation." Having armed American troops on the ground anywhere, he said, is a sensitive matter. "Dressing like the CTS," he added, "helps prevent any backlash for U.S. forces actively engaging in the fight."

It also helps conceal their numbers during patrols and could reduce the risk of a "blue-on-blue" attack, Emerson said, referring to incidents of mistaken identity that have led to friendly forces firing on one another.

Counter terror service units are widely seen as the security forces' most capable, having been trained for many years by American special operations teams. The personnel are a mix of special operations "Golden Brigades" and the federal police's rapid-response force, which functions like a SWAT unit. The CTS reports directly to Iraq’s prime minister.

These troops have demonstrated, by and large, an ability to resist the sectarian prejudice that continues to plague many conventional military and police units. The CTS played major roles in the successful liberation of Fallujah, Ramadi and Rutbah. And for that reason, they've been very active inside Mosul, where an estimated 2,000 ISIS fightersremain.

U.S. military officials say it's evident that progress continues — whatever the pace — as the Iraqis and their American advisers push deeper into western Mosul. Maj. Gen. Joseph Martin, the U.S Army commander who oversees coalition ground forces in Iraq, told Military Times during an interview last month that while he is confident ISIS will be pushed out, there are vast challenges associated with this type of urban combat.

He compared Mosul's size to that of Philadelphia: more than 200,000 dwellings, 1,800 miles of streets and roadways and 1.2 million people spread throughout the city. The Islamic State, Martin said, has had two years to prepare its defenses. "Two years to place caches in the ground, dig tunnels, use buildings that they want to use," he told Military Times. ISIS understands the terrain and is willing to exploit the population.

This dynamic is forcing the coalition to be patient and to adapt. For those reasons, he said, it's impossible to put a timeline on the Islamic State's full defeat in Mosul. "It's a level of complexity," the general added, "that I've never seen before."

Andrew deGrandpre is Military Times' senior editor and Pentagon bureau chief. On Twitter:@adegrandpre

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With additional reporting by Military Times staff writer Shawn Snow. On Twitter: @SnowSox184

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