Kenyan officials vowed not to bow to Al Shabaab after the terrorists struck at a college in a dawn attack on Thursday and killed 147 people, mainly students, and injured 79 others.

The Kenya Police Service said the attack lasted 12 hours and involved five militants, four of whom were killed and one arrested as he fled the scene.

“After initial breach of the university compound, the militants shot and killed two security guards manning the gate before proceeding to the student’s hostels area, where they took an unknown number of students hostage,” Interior Cabinet Secretary Joseph Nkaissery said at Garissa University College, the scene of the attack.

The internal security minister added that 500 people were rescued and 166 unaccounted for. The constituent college of Moi University has 815 students and 60 members of staff.

Newly appointed Inspector-General of Police Joseph Boinnet ordered a dusk-to-dawn curfew in four counties bordering Somalia — Wajir, Mandera, Garissa and Tana River.

The Al Shabaab claimed responsibility for the attack, saying it was in retaliation for the presence of Kenya Defence Forces in Somalia. Kenyan troops entered Somalia in October 2011 in an effort to stop the Islamists from crossing the long, porous border and kidnapping people, which was seen as a threat to tourism.

“Kenya is at war with Somalia, and unless they withdraw their troops, then we will continue with these attacks,” Al Shabaab spokesman Sheikh Ali Mohamud Rage said.

But Mr Nkaissery, a retired general, shot back: “Kenya will not bow to terrorist threats. We will not be intimidated by the terrorists who have made killing innocent people a way to humiliate the government. We shall win this war.”

Police sources said the militants engaged a security team that included the KDF in a fierce gun battle after they were cornered in an hostel. The attack ended in the evening when the four gunmen detonated their suicide vests amid a hail of gunfire.

President Uhuru Kenyatta said this was a moment for everyone to be vigilant as his government continued to confront and defeat Kenya’s enemies.

“I call upon the Inspector-General of Police to take urgent steps to ensure that 10,000 [police] recruits whose enrolment is pending promptly report for training,” President Kenyatta said in his national address. “I take full responsibility for this directive.”

The authorities also issued a $215,000 bounty for the capture of alleged Al Shabaab commander Mohamed Kuno, a former Kenyan madrassa teacher said to be the mastermind of the attack.