U.S. defense officials say the United States targeted a senior Islamic State commander in an airstrike last week in Syria and are assessing whether he may have been killed.

The officials said the target was Omar al-Shishani, a Chechen and one of the most prominent military leaders of the Islamic State. He is sometimes called Omar the Chechen.

The officials spoke on condition of anonymity because the attack has not been publicly announced and the outcome is in doubt.

The attack took place March 4 near the Syrian town of al-Shaddadeh, a former Islamic State stronghold that was captured in February by the U.S.-backed, predominantly Kurdish Syria Democratic Forces.