IRBIL, Iraq (AP) — Thousands of fighters flocked to join Iraq's state-sanctioned, Iran-backed Shiite militias on Sunday, advancing to cut off Islamic State extremists holed up near Mosul in northern Iraq while bombers killed at least 17 people in Shiite neighborhoods of Baghdad.
Militia spokesmen said that some 5,000 fighters had joined their push to encircle from the west the country's second-largest city of Mosul, the IS militants' last bastion in Iraq, which is linked by road to territory it holds in Syria.
Karim al-Nuri of the militias' umbrella group, known as the Popular Mobilization Units, and Jaafar al-Husseini, a spokesman for unit member the Hezbollah Brigades, said that a total of some 15,000 Shiite fighters were now participating in the battle.
The Iraqi military confirmed the figures, which, including army units, militarized police, special forces and Kurdish fighters would bring the total number of anti-IS forces in the offensive to over 40,000.
The two-week-old offensive to drive IS from Mosul had been long-anticipated, since the Sunni extremists stormed into the city in 2014 and drove out a much larger Iraqi force, albeit one that was demoralized from neglect and corruption.
Troops are now converging on the city from all directions, although most fighting is still taking place in towns and villages on Mosul's outskirts. The operation is expected to take weeks, if not months.
The Popular Mobilization Units say they will not enter Mosul itself and will instead focus on retaking Tal Afar, a town to the west that had a Shiite majority before it fell to IS in 2014. They acknowledge having help from Iranian military advisers.
Iraqi forces moving toward the city have made uneven progress since the offensive began on Oct. 17. They are four miles (six kilometers) from the edge of Mosul on the eastern front, where Iraq's special forces are leading the charge. But advances have been slower in the south, with government forces still 20 miles (35 kilometers) from the city.
The U.S. military estimates IS has 3,000 to 5,000 fighters inside Mosul and another 1,500-2,500 in the city's outer defensive belt. The total number includes around 1,000 foreign fighters.
In the hours following the announcement of Shiite reinforcements, five explosions rocked predominantly Shiite neighborhoods of the capital, Baghdad, killing at least 17 people and wounding over 60, police said.
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 10 and wounding 34. Other attacks hit the northern Shaab neighborhood, as well as traders' markets in the Topchi and Zataria areas as well as the poorer Sadr City district.
The officials spoke on condition of anonymity because they weren't authorized to brief reporters.
There was no immediate claim of responsibility for the blasts. But IS has stepped up its attacks in response to the offensive in Mosul, and it was possible the group was targeting Shiite areas in retaliation for the Mosul offensive.
Meanwhile, the Iraqi air force said it had landed a C-130 transport aircraft at Qayara air base, on the southern approach to Mosul, opening a key resupply route. IS forces had been leaving explosive booby-traps to slow the advance on Mosul, and the announcement suggested the airstrip was now cleared of such danger.
Earlier, Turkey's president warned that his government will be closely monitoring the Shiite militias' behavior in northern Iraq and seek to safeguard the rights of ethnic Turkmens there.
In statements carried by the state-run Anadolu agency, Recep Tayyip Erdogan told reporters that the militia group could prompt a Turkish response if it "terrorizes" the Iraqi-Turkmen town of Tal Afar, where it is headed in its push around Mosul.
"Tal Afar is an entirely Turkmen town. If Hashd al-Shaabi starts terrorizing it, then our response will certainly be different," Erdogan said, referring to the militia umbrella group in Arabic.
The involvement of the Iranian-backed Shiite militias has raised concerns that the battle for the Sunni-majority city could aggravate sectarian tensions. Rights groups have accused the militias of abuses against civilians in other Sunni areas retaken from IS, accusations the militia leaders deny.
At a camp on the outskirts of Kirkuk, some 100 miles (160 kilometers) from Mosul, around 600 displaced Sunni Turkmen families from Tal Afar were anxiously hoping IS will be driven from the city so they can head home soon.
"I escaped because of IS," said Hussna Abbas, 75, who was comforting her grandson as residents reported IS was firing intermittently toward their camp, known as Yahyawa. "They took one of my sons and they killed another one," she said. "God willing, God will return us to our homes."
Rohan reported from Baghdad; Cinar Kiper reported from Istanbul and Mstyslav Chernov from Kirkuk.