Security force personnel will vote in the country's parliamentary election on October 8 in locations where they are stationed, two days ahead of the main poll, in which citizens will vote in their home constituencies.

A statement Saturday by the electoral commission sought to explain why members of the Hashed al-Shaabi -- a militarily and politically powerful network numbering 160,000 personnel -- will have to vote in the main ballot on October 10.

It said it had contacted Hashed officials repeatedly seeking lists of fighters so as to include them in the special vote.

"The Hashed's authority did not give us the enrolled names, so the commission has included them in the general vote," the commission said.

Voting in home regions could prove challenging for many personnel stationed in geographically distant locations.

A spokesman for one key Hashed group, the Kataeb Hezbollah, said late Saturday that the measure "deprived fighters of their right to choose who will represent them and protect them from those who seek to weaken them".

Ahmed Assadi, a Hashed lawmaker complained "our brothers in the Hashed-al-Shaabi have been deprived of their special vote (rights) -- they will only be able to vote if they leave their stations and return to their (home) regions," in a statement published on social media Sunday.

The lawmaker called on his supporters to turn out en-masse "to compensate for the (lost) votes of our heroes who defend their positions".

The Hashed, which includes dozens of mainly pro-Iran Shiite groups, was created in 2014 to fight the Islamic State group, as the regular military failed to stem a lightning advance that allowed the jihadists to seize a third of the country.

The main Hashed coalition counts for 48 lawmakers among the 329 parliamentary seats.

They entered the legislature for the first time in the 2018 vote, after contributing hugely to the defeat of IS.

Opposition activists accuse Hashed armed groups of being beholden to Iran and an instrument of oppression against critics.

Alongside security force personnel, prisoners and displaced people will also vote in the special October 8 exercise.

More than 25 million citizens are eligible to vote in total in this month's poll, brought forward by a year to appease a protest movement that started two years ago but subsequently dwindled.