Somali militants have killed nearly 150 students, mostly Christian, in Thursday's deadly attack on the Garissa University College, Garrissa, Kenya.

According to Kenyan authorities, the attackers, Somali al-Shabab militants between four and 10 in number, invaded the school around dawn.

They moved from hostel to hostel, separating Christian students from their Muslim colleagues.

They then killed the Christians, shooting some in the head and beheading others..

A witness told CNN that the gunmen first stormed a Christian prayer service, killing some students and taking others hostage after which they rampaged across the campus, shooting non-Muslims, sparing Muslims.

Following the attack, al-Shabab said that its fighters attacked the university, separating Muslims from non-Muslims in an “operation against the infidels.”

The attack has been described as the worst terrorist attack since the 1998 bombing of the United States Embassy and the September 2013, Westgate mall attack that left 67 people dead and several others injured.

Al-Shabab's constant attacks have damaged Kenya’s tourist industry, forcing the government to consider building a 424-mile wall across the entire Somali border, according to New York Times.

Internally, the militant's habit of targeting Christians is further driving apart the minority Muslims, who claim persecution, and the majority Christians, who feel under attack.

The United States has issued a statement condemning the attack and pledging its continuous support in fighting the terrorists.

Garissa University College is in the town of Garissa, about 90 miles from the Somali border.