Ethnic Kurds are helping members of the Islamic State group in the battle for the key Syrian Kurdish town of Kobani, sharing their knowledge of the local terrain and language with the extremists, according to Iraqi and Kurdish officials.
It is not clear how many Kurds are aiding the estimated 3,000 IS militants in the Kobani area - and fighting against their own Kurdish brethren - but activists say they are playing a major role in the seven-week conflict near the Turkish border.
A senior military commander for the extremists in the town is an Iraqi Kurd known as Abu Khattab al-Kurdi.
Officials with the main Syrian Kurdish force known as the People's Protection Units, or YPG, say they became aware of the Kurds among the mostly Sunni Muslim extremists early in the fighting.
As Kurdish fighters were defending the nearby village of Shiran in September, two Kurdish men with different accents and wearing YPG uniforms infiltrated their ranks, Kurdish officials said. After being questioned, they were captured and admitted to fighting for IS, the officials said.
Iraqi and Kurdish officials say many of the Kurdish fighters with IS are from the north-eastern Iraqi town of Halabja, which was bombed with chemical weapons by Saddam Hussein's forces in 1988, killing 5,000 people.
Shorsh Hassan, a YPG spokesman in Kobani, said although most of the Kurdish jihadi fighters come from Iraq, some are from Syrian regions such as Kobani, Afrin and Jazeera. He added that the number of Syrian Kurds is small compared with the dozens of Iraqis fighting with the IS group.
"The fighter who is from Kobani is not like someone who hails from Chechnya with no idea about tracks and roads," Mr Hassan said.
Thousands of militants from all over the world - including north Africans, Asians and some Westerners - have travelled to Syria and Iraq to join the IS ranks. Turkish nationals are among them but it is unknown if any are fighting in Kobani.
Mr Hassan said many of the Iraqi fighters were from Halabja, including al-Kurdi. Websites affiliated with IS recently published several photographs of the young, bearded man, including some of him wearing the traditional Kurdish garb of baggy pants, and others of him standing in front of Kurds killed in Kobani.
In Baghdad, an Iraqi security official said al-Kurdi was a member of Ansar al-Islam, a Sunni militant group with ties to Abu Musab al-Zarqawi, the late leader of al Qaida in Iraq, who was active in the early 2000s. Al-Kurdi later joined IS, the official said.