FIVE people have been arrested on suspicion of involvement in the university massacre which left nearly 150 people dead, as Islamist militants al-Shabab threatened a "long, gruesome war" against Kenya which would see the nation's cities run 'red with blood'.

Kenyan Interior Ministry spokesman Mwenda Njoka said that security agencies had arrested three people trying to cross the border into Somalia following the 13-hour siege at Garissa University College, which killed 148.

The campus is around 120 miles from the Somali border.

The three suspects are associates of Mohamed Mohamud, also known as Dulyadin Gamadhere, a former teacher at a Kenyan Madrassa Islamic school who authorities say co-ordinated the assault on Garissa on Thursday by al-Shabab gunmen.

A further two suspects had already been arrested at the college, while the authorities put the bullet-ridden and swollen corpses of four dead gunmen on public display on Saturday in the hope that hundreds of locals might identify them.

Kenyan authorities have also put a $220,000 (£147,000) bounty for information leading to Gamadhere's arrest.

It came as al-Shabab has since pledged a "long, gruesome war" against Kenya which would see its cities run "red with blood".

The al-Qaeda aligned militant group said its attacks were in retaliation for acts by Kenya's security forces, who are part of the African Union's mission in Somalia against al-Shabab.

In a message directed at the Kenyan public, al-Shabab said: "No amount of precaution or safety measures will be able to guarantee your safety, thwart another attack or prevent another bloodbath from occurring in your cities," the group said in an emailed statement received by Reuters in the Somali capital.

It added: "This will be a long, gruesome war of which you, the Kenyan public, are its first casualties."

Meanwhile, a survivor of the Garissa killings was also discovered on Saturday after spending two days hiding in a cupboard at the college.

Cynthia Charotich, 19, said from her hospital bed today that she had covered herself with clothes and refused to emerge even when some of her classmates came out of hiding at the demands of the gunmen.

Kenyan officials said she was rescued shortly before 10am.

Charotich said she did not believe that rescuers urging her to come out of her hiding place were there to help, suspecting at first that they were militants.

Police have been on the scene at Garissa taking fingerprints from the bodies of the four assailants and of the students and security officials who died, for identification purposes.

The north-eastern Kenyan town lacks the facilities to store all the bodies.

In Nairobi, Kenya's capital, family members were lining up at a morgue where about 20 bodies had already been airlifted from Garissa.

Survivor Helen Titus said the assailants had targeted Christians by heading to a lecture hall where worshippers were gathered for early-morning prayer.

Titus, a 21-year-old English literature student who suffered a bullet wound to her wrist, said she had covered her face and hair with the blood of classmates and lay still in hopes that the gunmen would believe she was dead.

The masked gunmen, who were strapped with explosives and armed with AK-47s, told students hiding in dormitories to come out, assuring them that they would not be killed, said Titus.

"We just wondered whether to come out or not," she said.

Many students did, whereupon the gunmen started shooting men, saying they would not kill "ladies", Titus added.

But they also shot women and targeted Christians, said Titus, who is a Christian.

Al-Shabab, meaning "the youth", has been blamed for a series of attacks in Kenya, including the siege at the Westgate Mall in Nairobi in 2013 that killed 67 people.