"Based on accurate intelligence, an air strike was carried out by the international coalition targeting the number two in the Daesh terrorist organisation Abu Alaa al-Afari," the ministry of defence said in a statement.
Daesh is an Arabic acronym for the Islamic State organisation, which took over swathes of Iraq last year.
It was not clear from the statement whether Afari was killed in the strike, which the ministry said targeted a gathering in the Martyrs' Mosque in Tal Afar's Al-Ayadiya district.
Afari's name emerged last month in reports claiming that IS head Abu Bakr al-Baghdadi was incapacitated in a coalition strike and handed over the helm of the organisation to Afari.
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The Pentagon however said there was no reason to think Baghdadi had been wounded.
The structure of the organisation's senior leadership is secretive and IS has only released video or audio recordings of Baghdadi or the group's official spokesman Abu Mohammed al-Adnani.
Tal Afar lies near the border with Syria, almost 400 kilometres northwest of Baghdad, and was one of the first places IS fighters took over when they launched a surprise offensive on June 9 last year.
The US state department last month put a USD 7 million bounty on information leading to Afari, who is presented on the Rewards for Justice website under the name of Abd al-Rahman Mustafa al-Qaduli.