The victims prayed to Jesus and it cost them their lives.

An eyewitness of the deadly assault by Somali Islamist militants on a Kenyan university spoke on Friday of three female students he saw executed as they begged for mercy.

Reuben Mwavita, 21, a student, said the three were kneeling in front of the gunmen, praying for help.

"The mistake they made was to say 'Jesus, please save us', because that is when they were immediately shot," Mwavita told Reuters.

During Thursday's attack, in which at least 147 people died, al Shabaab gunmen at first killed indiscriminately. Later, though, they divided non-Muslims from Muslims.

"I was confused, I was terrified and was shaking, but I was not screaming and that is what saved me," said Susan Kitoko, 24, from the hospital, where she was nursing bruises and a broken hip from escaping through a window.

"The attackers were just in the next room, I heard them ask people whether they were Christian or Muslim, then I heard gunshots and screams."

Others also spoke of harrowing escapes from the killing.

"There were many gunshots mixed with screams. I heard men shouting saying 'We are al Shabaab, we are al Shabaab, we have paid you a visit tonight'... Four of us in our cube ran and jumped through the window from the first floor and went through the barbed wire fence," said Tony Otiende, 22, a student at the campus.

The college's Christian Union may have taken a lot of the brunt because of an early prayer meeting in the hall.

"They killed all my friends. I was praying with them when we heard gun shots and two guys who wore hoods and carried long guns came in. I escaped because I was standing next to the rear door, so I dashed out with one other friend," Kenneth Luzakula, a Christian Union student, told Reuters.

"I could hear my friends still praying loudly and calling the name of Jesus Christ," he said. "Others were screaming. I heard gunshots repeatedly from the toilet nearby where we had hidden. They killed my friends but I know they are all in heaven, because they died because they died worshipping God."

He said he lost more than 20 friends in the attack.