A former French Legionnaire who rose through the ranks of the Islamic State extremist group has been named by the U.S. as a key figure in the Nov. 13, 2015, attacks in Paris and those in Brussels and the leader of a 300-strong brigade of foreign jihadis.

The French are circumspect on the role of Abdelilah Himich, who was among three Islamic State figures designated Tuesday as terrorists by the U.S. government. His name does not appear in the Nov. 13 legal file, according to the Paris prosecutor's office.

Himich is believed to be the 'Abu Souleymane' referred to by some of the Nov. 13 attackers.

One French expert believes Himich's role was significant, but said he fell into disfavor soon after the March 22 attacks in Brussels and was jailed by Islamic State.