Thousands of Iraqi-Shia fighters mass outside Mosul

Some 5,000 fighters from Iraqi-Shia militias have joined the government push to encircle the country's second-largest city of Mosul and cut off Islamic State group fighters.

It comes as suspected IS bombers killed at least 17 people in residential Shia neighbourhoods in Baghdad.

Killing fields

Karim al-Nuri of the umbrella group for the militias - known as the Popular Mobilisation Units, or Hashd al-Shaabi - and Jaafar al-Husseini, a spokesman for unit member the Hizballah Brigades (not affiliated with the Lebanese-Shia militia) said that some 15,000 Shia fighters were participating in the battle.

The Iraqi military confirmed the figures, which, including army units, militarised police, and special forces bring the total number of anti-IS fighters in the offensive to over 40,000.

Mosul is Iraq's second-largest city and the last major bastion of IS fighters in the country.

The struggle to kick out the extremists has been long-anticipated since they stormed into the city in 2014, driving out a much larger Iraqi force, albeit one that was demoralised from neglect and corruption.

The involvement of the Iranian-backed Shia militias has raised concerns that the battle for the Sunni-majority city could aggravate sectarian tensions.

Fighters from the group have been accused of killing, kidnapping and torturing civilians in other Sunni areas retaken from IS. Human Rights groups have also accused the militias of running secret detention centres for suspected IS members or opponents.

The US military estimates IS has 3,000 to 5,000 fighters inside Mosul and another 1,500 to 2,500 in the city's outer defensive belt. The total number includes around 1,000 foreign fighters.

Explosions

In the hours following the announcement of the Shia reinforcements, five explosions rocked predominantly Baghdad.

Police officials said the deadliest of the bombings, a parked car bomb, hit a popular fruit and vegetable market near a school in the northwestern Hurriyah area, killing at least ten and wounding 34.

Other attacks by improvised explosive devices hit the northern Shaab neighborhood, as well as traders' markets in the Topchi and Zataria areas as well as the poorer Sadr City district.

Earlier, Turkey's President Tayyip Recep Erdogan warned that his government will be "closely monitoring" the Shia militias' behaviour in northern Iraq and seek to safeguard the rights of ethnic Sunni Turkmens there.

Erdogan told reporters that the Shia militia group could prompt a Turkish response if it "terrorises" the Iraqi-Turkmen town of Tel Afar, where it is headed in its push around Mosul.

"Tel Afar is an entirely Turkmen town. If Hashd al-Shaabi starts terrorising it, then our response will certainly be different," Erdogan said.

Meanwhile, military officials reported that an army helicopter had crashed in the central province of Salahuddin due to a technical malfunction. They said that the two pilots of the helicopter, which went down the previous evening, were missing.