The leader of Islamic State in Syria, one of the top five leaders of the militant group, has been killed in a U.S. air strike, the U.S. military said on Tuesday, writes the Reuters.

In a statement, U.S. Central Command said Maher al-Agal had been killed in a drone strike in northwesten Syria and a close associate of his was seriously injured.

"Extensive planning went into this operation to ensure its successful execution. An initial review indicates there were no civilian casualties," the statement added.

It said al-Agal was responsible for developing ISIS networks outside of Iraq and Syria.

Reuters had earlier reported on the killing, citing U.S. officials.