BAGHDAD — The Iraqi government said Wednesday that the second-in-command of the Islamic State had been killed in an airstrike carried out by the American-led coalition in northern Iraq, a claim American officials said they could not confirm.

Iraq’s Ministry of Defense said that the militant leader, known as Abu Alaa al-Afari, was killed in a strike near the northern city Tal Afar. The United States Central Command acknowledged that airstrikes were conducted against the Islamic State, also known as ISIS or ISIL, near Tal Afar on Tuesday and Wednesday, but it could not verify the government’s claim.