Al-Shabab, the Somali armed group that carried out a deadly attack on a Kenyan university killing 148 people on Thursday, has threatened to stage more attacks in the country.

In a statement issued on Saturday, the group warned Kenyans that their cities will "run red with blood".

"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 statement read.

Four al-Shabab fighters stormed the Garissa University College campus in what appeared to be an extensively planned out attack, which the group says was to avenge Kenya's involvement in Somalia.

Kenya's interior ministry said the dead included 142 students, three policemen and three soldiers.

The ministry said on Saturday that five men - suspected accomplices - were arrested in connection with the attack.

Surviving students have been taken to a military camp, waiting to be bussed home as the university has been indefinitely closed.

Christine Onyongo, one of the survivors, told Al Jazeera that she had heard the attackers threatening female students that they would be burnt. Women were then let out, holding their hands up.

She said the men were treated more harshly, "especially those who were arguing".

"They were just slaughtering them," she said..

Like many other students, Onyongo said she would not come back to Garissa.

"After what I saw, not me - I can't come back."

Survivor found

A clean-up operation was going on as security personnel searched the university complex for more survivors and bodies on Saturday.

From the scene: Al Jazeera's Catherine Wambua-Soi

Forensic investigations are still going on as well as a massive clean-up. Eyewitnesses we spoke to who've been inside the compound told us of a bloody scene - furniture strewn around, grenade parts, spent cartridges, blood everywhere. It's hard to imagine the chaos and the horror of the hostages, many of whom died. We’ve been seeing national youth service going in with fire extinguishers and water bowsers to clean up. Police are still combing the grounds for possibly more survivors and bodies. 

A female student, 19-year-old Cynthia was found alive.

"I just hid on top of a wardrobe the whole time. I could hear them shouting and shooting," she told Al Jazeera. "At some point they came to our hostel and took two of my friends. I just hid and hid and when I got hungry ate some body lotion that was in a paper bag." 

The attack, in which all four assailants were killed, was the deadliest on Kenya's soil since the 1998 bombing of the US embassy in Nairobi, which killed more than 200 people. 

Kenya sent troops to Somalia in 2011 following cross-border raids and attacks on its coastal towns blamed on al-Shabab.

In September 2013, 67 people were killed as al-Shabab besieged a shopping mall in Nairobi.

Anger over the Garissa massacre was compounded by the fact there were warnings last week that an attack on a university was imminent. Local residents accused the authorities of doing little to boost security in the little-developed region.

Garissa resident Kabange Kimani said there had been promises of increased security before.

"An attack happens, we are reassured of security. Security will be beefed up. Some high-profile figures will come from Nairobi. They land here for a few hours and go back, only for this thing to happen a few days later," he told Al Jazeera.

But Nathif Adam, the governor of Garissa county, said the government is doing its best. 

"I think it's not fair to say that security is not doing well," Adam told Al Jazeera. "I can confidently say that the Kenya security team and officials are doing their best possible. The only unfortunate thing is that here you're fighting guerrilla type terrorism which can attack anytime, anywhere.

"The level of preparedness of government is adequate [...] but this is an international terrorist group."

Source: Al Jazeera