BAGHDAD (Reuters) - Islamic State fighters traded sniper fire and mortar rounds with Iraqi troops and allied Shi'ite militia forces on Sunday in the city of Tikrit amid further reports the militants had obtained chlorine for possible use as a chemical weapon.
A military official returned from the front in Tikrit said no major advances were made by either side nearly two weeks into an operation to win back the city IS fighters seized last June.
Iraqi Kurdish authorities said on Saturday they had proof the radical Islamist militants occupying large parts of the country's north and west used chlorine against Kurdish peshmerga fighters in January in a car bombing attempt west of the city of Mosul.
The Baghdad government has not issued a statement on the semi-autonomous Kurdish region's announcement. An official reached by Reuters on Sunday declined to comment.
But the mayor of a town on the northern edge of Tikrit told Reuters on Sunday that storage containers filled with chlorine were found by troops and mainly Shi'ite militiamen when they entered al-Alam last week, the day before they fought their way into Tikrit.
"We found a number of storage units containing chlorine that we think were seized by Daesh from water purification stations in different parts of Tikrit," Laith al-Jubouri said, using the Arabic acronym for the group. He said security forces had sealed off the area where the containers were found and alerted Baghdad authorities.
He also said the security forces had found bombs containing chlorine.
On Tuesday, when Iraqi forces and allied mainly-Shi'ite militias pushed Islamic State fighters out of the town, a Reuters photographer was present when Iraqi police instructed journalists to stand back and hold their breath as they detonated a roadside bomb they suspected contained chlorine.
When they detonated the bomb, a yellowish plume burst into the air, and as bystanders coughed, officials shouted "be careful, it's chlorine!", the Reuters photographer said.
The statement from Kurdish authorities about Islamic State's use of chlorine referred to footage of "similar attacks" during the recent fighting around Tikrit, though the mayor and another security official only noted the presence of chlorine found in areas recently seized back from IS.
The military campaign to retake Tikrit has been stalled since Friday, when security officials said Iraqi forces and their militia allies would wait for reinforcements before moving forward.
Two days later, back-up had not yet arrived, and officials continued to stress the challenges they faced in flushing out militants in street-by-street battles and defusing bombs and booby traps they laid while retreating from parts of the city.
"There were no new pushes today from either side, only scattered skirmishes in the northern and southern parts of the city," Colonel Mohammed Abid al-Jubouri told Reuters by phone after visiting the southern edge of Tikrit on Sunday.
Jubouri said the process of "organizing troops and waiting for reinforcements" was ongoing and did not say when a fresh effort to seize the central districts of the city still held by IS would begin. The militants still hold about half the city, which lies about 160 km (100 miles) north of Baghdad.
Most residents of Tikrit fled in the months after the extremists overran the city in June.
Fabio Forgione, Head of Mission for Doctors without Borders, said his organization was concerned about the "huge number of civilians" in areas north of Tikrit where fighting could shift after the current offensive.
The effort to retake Saddam Hussein's home city from the militants has been the biggest offensive yet against the group that has declared an Islamic caliphate on territory it controls in Iraq and neighboring Syria.
To the southeast near the Shi'ite city of Samarra, a suicide bomber drove a car into a group of Shi'ite militiamen, killing three of them, police and medical sources said. The militia groups have been using Samarra as a rear base for the Tikrit offensive.
Atrocities committed by Islamic State continue to surface. More than 50 corpses were found on Sunday near the mainly Shi'ite Turkman town of Bashir near Kirkuk in northern Iraq, said Kamil Amin, spokesman for Iraq's Human Rights ministry.
He said experts from the Human Rights and Health Ministries also visited three mass graves recently found near the village of Abu Ajeel, east of Tikrit, on Sunday. The experts took one corpse as sample to do analysis to determine whether they were the victims of a massacre of Iraqi soldiers of unprecedented scale at Camp Speicher in June.
Additional reporting by Isabel Coles in Arbil and Maggie Fick in Baghdad; Writing by Maggie Fick; Editing by Rosalind Russell and Giles Elgood