At least 147 people died in an attack on the Garissa University College campus by al-Shabab gunmen.
The four gunmen, who initially besieged the campus, targeting Christian students for executions, blew themselves up as the siege ended according to the Associated Press.
UN Secretary-General Ban Ki-moon condemned what he called a "terrorist attack" and said the UN was ready to help Nairobi to "prevent and counter terrorism and violent extremism".
The United States said it was offering the Kenyan government assistance to take on al-Shabab and would continue to work with others to take on the group.
According to AP, student Collins Wetangula said when the gunmen entered the hostel he could hear them opening doors and asking if the people inside were Muslims or Christians.
"If you were a Christian you were shot on the spot. With each blast of the gun I thought I was going to die," he said.
Al-Shabab says it attacked the university because it is at war with Kenya, BBC Africa analyst Mary Harper reports.