Three Edmonton cousins have died while fighting overseas for ISIS, says the father of one of the men.

Ahmed Hirsi says his 20-year-old son, Mahad, was killed last fall along with cousins Hamsa and Hersi Kariye.

Another cousin from Minnesota, Hanad Abdullahi Mohallim, was also killed, Hirsi said.

Other family members deny the men died while fighting for ISIS, but Hirsi insists it's true.

He said his son and two nephews left Edmonton without telling him in October 2013.

He heard from Mahad for the last time when he called from Egypt saying he intended to leave for Syria.

Hirsi's sister Mulki Hirsi Hassan called him last fall to break the news that all four men had been killed, he said.

It’s not clear how the four died or if they died at the same time.

Family from war-torn Somalia

Hirsi said he can't understand how his son became radicalized.

Ahmed Hirsi

Ahmed Hirsi says he cannot understand how his son Mahad became radicalized. (CBC )

He brought his family to Canada from war-torn Somalia to live in a peaceful country, he said, and he doesn't know why his son and nephews joined ISIS.

Mahad was an obedient son, regularly attending school. He was generous and respectful but became unhappy with his faith, Hirsi said.

"Some people, I don't know who he is, they make him brainwash and they change his mind," he said.

At least one family member insists the men did not go overseas to join ISIS.

Guled, a brother of Hamsa and Hersi, said the men went to Egypt to pursue an education.

"That is the path my brothers wanted to take from Day 1," he said. "These people left their country to go study their religion."

He confirmed his brothers are dead but would not say how or where they died. He said the family has been co-operating with CSIS and the RCMP.

With CBC's Adrienne Arsenault, Nazim Baksh and Andrea Huncar