Kenyans have begun three days of national mourning and dedicated Easter Sunday prayer services to the 148 victims of the recent university massacre by al-Shabab fighters.

Easter ceremonies across the country were due to be held in the memory of the students and security personnel killed in a country where 80 percent of the population is Christian, with flags flying at half-mast.

President Uhuru Kenyatta has declared three days of national mourning after the attack in the northeastern town of Garissa, near the border with Somalia.

In the capital city of Nairobi, one candle was lit in memory of each victim of the attack on Garissa University College in a vigil on Saturday.

After besieging the university on Thursday, al-Shabab gunmen lined up non-Muslim students before executing them in the armed group's bloodiest attack to date.

The attack claimed the lives of 142 students, three police officers and three soldiers.

'Mindless slaughter'

Kenyatta pledged that the attackers would face justice for the "mindless slaughter" and vowed to retaliate in the "severest way" to the killings.

Five men have been arrested in connection with the attack. 

Al Jazeera's Catherine Wambua-Soi, reporting from Garissa, said that the president's statement was hard-worded and tough. 

"He said that many of the funders, organisers and recruiters for al-Shabab are in Kenya and are Kenyans," she said.

The massacre was Kenya's deadliest attack since the 1998 bombing of the US embassy in Nairobi.

On Saturday, al-Shabab warned of a "long, gruesome war" unless Kenya withdrew its troops from Somalia, and threatened "another bloodbath".

Hours after al-Shabab's warning, police in Garissa paraded four corpses of the gunmen piled on top of each other face down in the back of a pick-up truck followed by a huge crowd.

Police insisted the grim display was to see if anyone could identify the assailants, but some onlookers threw stones at the bodies as they passed, while others jeered and shouted at the dead.

Our correspondent also said that another objective of the display was to prove to Kenyans that the gunmen had indeed been killed, and to try and build public confidence in the security forces.  

In Nairobi's ethnic Somali district demonstrators took to the streets protesting against al-Shabab, echoing Kenyatta's call for unity in the country.

Kenya has suffered a series of attacks since 2011 when it sent troops to neighbouring Somalia to join African Union forces battling al-Shabab.

Source: Al Jazeera and agencies