Survivors of an attack that killed at least 22 college students in Nigeria's northeast say sabotaged phone lines prevented them from warning friends that could have saved lives.

John Bello, a student of the Federal Polytechnic Mubi, said Friday only one mobile phone network was working in the northeastern town of Mubi and that it was congested.

He said "we could maybe have alerted some of those that were killed if the networks weren't down."

Student Danjuma Aiso said he could hear gunshots for five hours. Police say 22 students and three others were killed.

The killings came a month after the radical Islamist sect, Boko Haram, attacked phone masts in Nigeria's northeast that crippled communications in the violence-torn region.

No group has claimed responsibility for the college killings.