At least four civilians were killed Monday in the army-held eastern side of Mosul by a chlorine gas attack by the ISIL terrorist group, according to an Iraqi security source.

"Three rockets fell in eastern Mosul’s Al-Hadba district, killing four civilians and injuring six others, including women and children,” Police Lieutenant-Colonel Ahmad Abdul-Aziz al-Numani told Anadolu Agency. 

"A preliminary report by medical workers at the scene confirmed that victims had suffered suffocation and burns usually associated with chlorine gas exposure," he said. 

Al-Numani added that Iraqi security officials had taken samples of the rocket debris and were now in the process of testing them "to ascertain the nature of the attack".

He asserted: “We hold ISIL responsible for this attack, which our sources confirm originated from the ISIL-held western side of the city.” 

In January, Iraqi forces drove ISIL terrorists from eastern Mosul as part of a wide-ranging campaign launched late last year to retake the city, which ISIL overran in mid-2014. 

In mid-February, Iraqi forces -- backed by U.S.-led air power -- began a fresh push to recapture western Mosul, the terrorist group’s last stronghold in northern Iraq.