Two soldiers were also killed in the military offensive, which started Monday. Their identities were withheld pending notification of their families.
Two Scout Rangers, Cpl. Eric Jacosalem and Pfc. Leo Navales, were also wounded in the fighting.
Maj. Gen. Cristolito Balaoing, commander of the Army’s 4th Infantry Division, said Arimao Solaiman Lucsadato, alias Commander Syria was killed Tuesday by Scout Rangers under Col. Armando Cunanan during a firefight in Barangay Liningding.
Syria, assistant division commander of the 5th division of the Bangsamoro Islamic Armed Forces, was one of those who led the MILF attack on Maigo town last April 24.
Syria was the brother of Yahyah Lucsadato, a fugitive MILF commander.
The 37 other dead rebels have not been identified.
Troops found an arms cache consisting of firearms, explosives and ammunition at the scene of the fighting.
Armed Forces chief Gen. Narciso Abaya warned that more civilians would have to leave their homes as troops continue to attack MILF positions.
Some 17,000 civilians or about 4,000 families have fled their homes in Maligo and Munai towns in Lanao del Norte following the military offensive, he added.
Abaya said the actual number of evacuees was less than what the military had earlier estimated.
"We have estimated more than what is reported right now but again the operations are still ongoing," he said in a television interview Tuesday. "There might be some additional evacuees."
Abaya said that there is always the danger of accidentally hitting non-combatants in any armed conflict despite intelligence information to pinpoint the actual target.
"In some cases we have to forgo bombing certain areas especially when it’s very close to population centers (but) there’s no assurance," he said.
"In any armed conflict, there’s always the danger of hitting unintended targets."
Abaya said the Department of Social Welfare and Development and other non-government organizations are ready to help the evacuees.
"Because of past experiences, we take into consideration those implications of our tactical operations," he said.
Lt. Gen. Rodolfo Garcia, Armed Forces vice chief of staff and spokesman, said the military offensive against the estimated 300 MILF fighters led by Abdulrahman Macapaar, alias Commander Bravo, and Yayah Lucsadato will continue until they are captured. –Bong Fabe, Lino dela Cruz, Ann Corvera, James Mananghaya, John Unson, Mike Frialde, Perseus Echeminada, Roel Pareño