Smoke rises after clashes at Qadisiyya neighborhood in Tikrit, 80 miles north of Baghdad Saturday. (Khalid Mohammed/AP)

Kurdish authorities in Iraq said Saturday they have evidence that the Islamic State used chlorine gas as a chemical weapon against peshmerga security forces, the latest alleged atrocity carried out by the extremist organization.

Meanwhile, Iraqi security forces continued to engage in fierce clashes with the militants on Saturday as they continued their offensive to retake Saddam Hussein’s home town of Tikrit.

Those Iraqi forces, which include the military, police, Shiite militias and Sunni tribesmen, entered the city of Tikrit for the first time Thursday, gaining control of neighborhoods on its northern and southern ends.

Militia commander Hadi al-Amiri has said security forces were holding their position on the edges of the city until the area is cleared of any remaining civilians. They plan to press forward toward the city center once reinforcements arrived.

The allegation by the Kurdistan Region Security Council, stemming from a Jan. 23 suicide truck bomb attack in northern Iraq, did not immediately draw a reaction from the Islamic State, which holds a third of Iraq and neighboring Syria in its self-declared caliphate. However, Iraqi officials and Kurds fighting in Syria have made similar allegations about the militants using the low-grade chemical weapons against them.

The Islamic State is one of the most well-funded terrorist organizations in the world. So where does it get its money? (Jorge Ribas/The Washington Post)

In a statement, the council said the alleged chemical attack took place on a road between Iraq’s second-largest city, Mosul, and the Syrian border, as peshmerga forces fought to seize a vital supply line used by the Sunni militants. It said its fighters later found “around 20 gas canisters” that had been loaded onto the truck involved in the attack.

Video provided by the council showed a truck racing down a road, white smoke pouring out of it as it came under heavy fire from peshmerga. It later showed a white, billowing cloud after the truck exploded and its remnants scattered across a road.

An official with the Kurdish council told the Associated Press that dozens of peshmerga were treated for “dizziness, nausea, vomiting and general weakness” after the attack. He spoke on the condition of anonymity as he was not authorized to discuss the incident.

The Kurds say samples of clothing and soil from the site were analyzed by an unnamed lab in an unnamed coalition-partner nation, which found chlorine traces.

“The fact ISIS relies on such tactics demonstrates it has lost the initiative and is resorting to desperate measures,” the Kurdish government said in the statement, using an alternate acronym for the Sunni militant group.

There was no independent confirmation of the Kurds’ claim.

Peter Sawczak, a spokesman for the Organization for the Prohibition of Chemical Weapons, which has monitored Syria dismantling its chemical weapons stockpile, said his group had not been asked to investigate the attack.

Alistair Baskey, a spokesman for the White House’s National Security Council, said American officials were aware of the Kurds’ claim, though they had no information “regarding its veracity at this time.”

“We find such allegations deeply disturbing, and if there are parties engaged in such use, they should be held appropriately accountable,” Baskey said.

— Associated Press