ISIS deputy leader Abdul Rahman Mustafa Mohammed, also known as Abu Alaa al-Afri, has been killed in a US-led coalition air strike in northern Iraq, the Iraqi ministry of defense says.

The second-in-command of Islamic State was inside a mosque in Tal Afar that was targeted, spokesman General Tahsin Ibrahim said.

Abu Alaa al-Afri had been meeting dozens of militants who also died in the strike, he added.

In recent weeks, there were unconfirmed reports that Abu Alaa al-Afri had taken temporary charge of ISIS operations.

Iraqi security sources claimed that ISIS leader Abu Bakr al-Baghdadi had been incapacitated as a result of a coalition air strike in northern Iraq in March.

Last week, the US state department offered a reward of up to $7 million for information on Abu Alaa al-Afri, whom it identified as Abdul Rahman Mustafa al-Qaduli.