Masked al-Shabab militants stormed dormitories at a university in eastern Kenya early Thursday, killing at least 147 people in the worst terror attack on Kenyan soil in nearly two decades, officials said.

More than 500 students were rescued after the Islamist militants, heavily armed and strapped with explosives, attacked the campus of Garissa University College about 5:30 a.m., shooting some young people and taking others hostage. At least 79 people were injured, according to Kenya’s National Disaster Operation Center.

A government spokesman said the siege ended after 15 hours, with four gunmen from the Somali group having been killed.