Al-Shabaab on Saturday threatened to launch more attacks in the wake of Thursday's massacre as Kenyan authorities track down and arrest suspected militants trying to flee across the border to Somalia, CBS News reported.

In a statement posted online, the Somali-based Islamist extremist group warned there will be more attacks like the one at Garissa University College that left 148 people dead.

"Kenyan cities will run red with blood," the group wrote, according to the intelligence monitoring group SITE. "This will be a long, gruesome war of which you, the Kenyan public, are its first casualties."

The extremists claim the assaults are in retaliation for Kenya sending troops across the border into Somalia to battle its members.

"No amount of precaution or safety measures will be able to guarantee your safety, thwart another attack or prevent another bloodbath," the militants said.

Five people have so far been arrested for their alleged involvement in the attack, Interior Ministry spokesman Mwenda Njoka said, according to CBS News.

Three of them- arrested while attempting to cross into Somalia- are associates of a man named Mohamed Mohamud, who allegedly orchestrated Thursday's assault that targeted Christian students. He is also known as Dulyadin Gamadhere.

A $200,000 reward is being offered for information that leads to his capture.

More details emerged Saturday about the attack, including false reports that the gunmen who stormed the university as students slept early Thursday morning were wearing suicide vests. Officials later said suicide vests were not used, the station reported.

Also on Saturday, a 19-year-old Christian student named Cynthia Cheroitich was rescued after spending two days inside a wardrobe.

She told the Associated Press she covered herself with clothing and refused to reveal herself as the gunmen demanded the students come out. At one point during her hiding, she downed a bottle of body lotion because she was so hungry.

"I was just praying to my god," Cheroitich told the AP.