Two female suicide bombers hidden among civilians fleeing the besieged town of Mosul, Iraq, have blown themselves up killing at least one person, the army has said.

The women had been sent on the suicide bombing mission targeting troops by the Isis terror group, Sgt. Ali Abdullah Hussein told AP. He added it is the fourth suicide bomb attack targeting troops to occur in the past few days.

The attack, unusual because Isis rarely uses female fighters, occurred close to the destroyed al-Nuri Mosque, which Isis demolished earlier in June as troops advanced.

The mosque was highly symbolic because it was used by Isis leader Abu Bakr al-Baghdadi to deliver his declaration of the establishment of the Isis caliphate (religious state), when the group emerged from the desert to seize Iraq's second city in 2014 and used it as a base to become an unprecedented global terror threat.

The Iraqi army, the Kurdistan Regional government and a US-led coalition are involved in what is known as the 'Battle for Mosul', a joint military offensive that began in October 2016.

The army recaptured eastern Mosul in January and is now fighting to retake control of the western part of the city. Troops are now advancing in the last pocket of territory held by the militants in Mosul's Old City neighbourhood.

It is believed Isis now controls just one square kilometre warren of alleyways in the city centre and the army estimates it can retake full control of the city in a matter of days. However, several previous timetables for the final defeat of the Isis hold-outs have been missed.

Indeed, Iraqis prepared to celebrate the expected victory over Isis on Sunday (2 July), with troops tying white banners and Iraqi flags to lamp posts and damaged buildings, Reuters reported. The government said it was planning a week-long celebration.