Nairobi has pledged to respond in "the severest ways" to the recent horrendous attack by the al-Qaeda-linked Somali militant group al-Shabab in eastern Kenya.

On Thursday, four militants from the group killed 148 people, 142 of them students, and wounded at least 79 at the Garissa university after a day-long siege.

"Our forefathers bled and died for this nation and we will do everything to defend our way of life," Kenyan President Uhuru Kenyatta said in a speech from the State House in the country’s capital on Saturday.

"Our task of countering terrorism work has been made... more difficult by the fact that the planners and financiers of this brutality are embedded in our community and (were) previously seen as ordinary harmless people," he said.

Al-Shabab militants have said the attack was carried out in revenge for Kenya’s military operations in Somalia. The group has also threatened more bloodshed.

"Our message will be written to you not with words, but with the blood of your people. Dig their graves and prepare their coffins now," it has said in a statement.

Survivor walks out after two days

A survivor of the killings was found two days after the attack. Nineteen-year-old Cynthia Cheroitich said she hid in a large cupboard and covered herself with clothes all this time, refusing to emerge even when some of her classmates came out of hiding at the demands of the gunmen from the al-Shabab group.

Arrests

Nairobi has announced the arrest of five suspects in connection with the massacre.

Three of the suspects were apprehended while trying to flee to Somalia, while the other two were apprehended in the university area, said Interior Ministry spokesman Mwenda Njoka.