Over 140 people were killed Thursday after militants from the Somali Islamist group al-Shabaab launched a vicious pre-dawn assault on a public university in the city of Garissa, Kenya, the Associated Press reported. 

Another 79 people were wounded at Garissa University College in an attack seen as retaliation for Kenya sending troops to battle extremists across the Somali border, which lies less than 100 miles from the city. The death toll is expected to rise.

An unknown number of al-Shabaab gunmen gained access to the campus by shooting the guards at the gate before making their way over to a building where Christian services were underway, police and witnesses told CNN.

The gunmen took Christian hostages and stormed the college dormitories, scarring students out of their sleep as their gunshots rang throughout the night. They began "shooting anybody they came across except their fellows, the Muslims," said Joel Ayora, who witnessed the 5 a.m. massacre.  

Many students were able to flee to safety at a Kenya Defense Forces camp, but many were unable to escape the gunmen as they continued shooting relentlessly "from all angles," said Nairobi blogger Robert Alai Onyango, CNN reported.

"We don't know how may there were, but there are probably more than 10," the blogger said. "We believe the attackers were wearing something close to military fatigues."

Kenya security forces arrived and were able to corner some of the militants, according to the Interior Ministry. Four of the hostage takers were killed. All staff members and about 500 of the university's 815 students have been accounted for.

Al-Shabaab's assault comes two years after it killed 67 people in an attack on a shopping center in Nairobi. The country's weak border with Somalia makes it easier for rebels to terrorize Kenyans, CNN noted.

"This is a moment for everyone throughout the country to be vigilant as we continue to confront and defeat our enemies," Kenyan President Uhuru Kenyatta said.