NAIROBI, Kenya -- Kenyan police Thursday charged five men with participating in an attack by militant group al-Shabab on a university in eastern Kenya in which 148 people were killed.

The five men pleaded not guilty to 152 counts of committing acts of terrorism in a Magistrates Court.

Four al-Shabab gunmen stormed the Garissa University College at dawn on April 2. The attack went on for hours before it was finally ended by a specialized police unit and the four gunmen were killed.

The prosecution alleges that the five suspects colluded to carry out the attack but have not said what their roles were.

Prosecutor Daniel Karuri urged the court to deny the suspects bail. Magistrate Daniel Ochenja directed that they be detained until June 11, when the court will determine whether they will be granted bail.

The five suspects complained they were tortured for 10 consecutive days as the anti-terrorism police tried to force confessions from them.

Speaking through an interpreter, the four Somalis and a Tanzanian claimed their heads were forced into buckets full of water, that they were electrocuted and whipped after they denied involvement in the attack in which 148 people, mainly students, were killed.

Al-Shabab has vowed to carry out attacks against Kenya for sending its troops to Somalia to fight the militants. Kenya has experienced a wave of explosive and gun attacks since October 2011 when its troops went into Somalia.

Late last month, the Kenyan government said an al-Shabab attack on a convoy of vehicles carrying 59 policemen left one officer dead.