US Central Command on Tuesday tweeted out photos of Syrian women fighters who have joined the campaign against ISIS in the country.

"Those photos were taken by CENTCOM's spokesman who travelled to Syria with Gen. Votel recently to visit with senior leaders of the Syrian Democratic Forces," a CentCom spokesman told Business Insider in an email.

—U.S. Central Command (@CENTCOM) February 28, 2017

—U.S. Central Command (@CENTCOM) February 28, 2017

—U.S. Central Command (@CENTCOM) February 28, 2017

While Central Command did not elaborate on which faction the women pictured belonged to in the tweets or in its email to Business Insider, one of the most prominent groups of women fighters in Syria are Kurdish rebels (though there are Kurdish women fighters in Iraq, as well).

The Kurdish militia known as the People's Protection Units, or YPG in its Kurmanji initials, has an all-women fighting unit called the Women's Protection Units, or YPJ.

The YPG is loosely organized with an egalitarian leadership and embraces radical leftist politics. Members of the organization use a gender-neutral moniker for each other — hevale — elects leaders directly, and "command positions are jointly occupied by a man from the YPG and a woman from the YPJ," Seth Harp reported for Rolling Stone in mid-February.

A Kurdish fighter from the People's Protection Units (YPG), operating with Syrian Democratic Forces, in the northern Raqqa countryside, November 14, 2016. REUTERS/Rodi Said

"[YPG] troops are lightly armed and go into battle without body armor or helmets or even boots, just sneakers and Kalashnikovs, wearing the black flowery headscarves typical of Rojava, which the men took up wearing in solidarity with the women," Harp writes.

The presence of women fighters on the front line against ISIS — whose horrific treatment of women is well-known — has, at times, attracted coverage that focused on the fact that they are women.

One story in late 2016 referred to a slain Kurdish fighter as "the Angelina Jolie of Kurdistan."

Some of those fighters, however, seem to have little interest in anything but the mission at hand.

"I like that when we kill them they lose their heaven," a 22-year-old figher named Haveen told The New York Times last spring. "I don't know how many of them I've killed. It's not enough. I won't be happy until they're all dead."