BAGHDAD: Hundreds of detainees in Iraq are feared to have been "forcibly disappeared" by Kurdish authorities after they were arrested for suspected ties to Daesh (ISIS), Human Rights Watch said Thursday.

"More than 350 detainees held by the Kurdistan Regional Government in the Iraqi city of Kirkuk are feared to have been forcibly disappeared," the U.S.-based rights group said in a statement.

Most of those missing are Sunni Arabs detained by the Kurdish Asayish security agency on suspicion of Daesh "affiliation" after Kirkuk was taken from the extremist in 2014, the statement said.

"Families in Kirkuk are desperate to know what has become of their detained relatives," said HRW's deputy Middle East director, Lama Fakih.

"The secret, incommunicado detentions raise grave concerns for their safety."

HRW said the disappearance of the detainees came to light after Iraqi government forces retook Kirkuk from the Kurds in October following a controversial independence referendum.

"Local officials told Human Rights Watch that the prisoners were no longer in the official and unofficial detention facilities in and around Kirkuk," the group said.

The fate of the missing people has already sparked protests from anxious relatives and drawn the attention of the authorities in Baghdad.

In November, Prime Minister Haider al-Abadi ordered an investigation after dozens of complaints from Arab families about relatives they say have not been heard from since their arrest by Kurdish forces.

Kirkuk and the surrounding oil-rich region are fiercely disputed between Baghdad and the autonomous Kurdish region.

The Kurds took part of the area after the U.S.-led invasion of 2003 and extended their control in the chaos that followed the lightning Daesh advance across Iraq in 2014.

Federal forces reclaimed Kirkuk and the oil fields around it after Baghdad rejected a vote by the Kurds for independence in September.