A senior commander of Iran's Islamic Revolutionary Guards Corps (IRGC) was killed fighting Islamic State (IS) group west of the Iraqi city of Mosul, the Tehran-based Tasnim news agency reported on Saturday.
It is the first time Iran has announced the death of a senior commander during the operations launched in October to drive the Islamist militants out of Mosul.
"Commander Shaaban Nassiri was martyred in operations to free the area west of Mosul," the Tasnim news agency quoted the Revolutionary Guards as saying.
The IRGC is the main backer of the Iraqi Shi'ite paramilitary force known as Popular Mobilisation, fighting Islamic State west of Mosul.
Nassiri was killed near Baaj, one of the last cities which remain under Islamic State control, near the Syrian border, according to Mashregh, an Iranian news website.
Baghdadi is believed to be hiding in this region, according to U.S. and Iraqi officials.
Nassiri fought in the Iran-Iran war of 1980-1988 and has been involved in the six-year war in Syria, backing President Bashar al-Assad, according to Mashregh.
A general from the Revolutionary Guards assumed the post of Iran's ambassador to Iraq in April, in a sign of the key role the military force is playing in its neighboring country.
Popular Mobilisation on Friday announced the capture of the Sinjar military base, near Baaj, moving its presence closer to the Syrian border.
Iraq's Shi'ite-led government is aiming to control the border in coordination with the Iranian-backed army of Assad.
Linking up the two sides would give Assad a significant advantage in fighting the six-year rebellion against his rule.
Iran has provided military support to Assad since at least 2012, but initially did not comment publicly on its role. But as the military support increased and Iranian casualties rose, officials began to speak more openly.
An Iranian official said late last year that more than 1,000 Iranians had been killed in the Syrian civil war. These include a handful of senior commanders of the Revolutionary Guards, according to Iranian media reports.
Iran has helped to train and organize thousands of Shi'ite militia fighters from Iraq, Afghanistan and Pakistan in the Syrian conflict. Fighters from Lebanon's Hezbollah are also working closely with Iranian military commanders in Syria.