Two security guards, one policeman and one soldier were also killed in the siege, which ended 15 hours after the gunmen launched their assault.

The four gunmen had strapped themselves with explosives which they detonated as soldiers burst into the dormitory where they were holed up, according to Interior Minister Joseph Nkaiserry.

Somalia's al Shabaab militant group has claimed responsibility for the pre-dawn attack, which is the country's deadliest since the US embassy bombings in 1998.

Student Michael Bwana, who managed to flee, said most of those taken hostage were girls.

Kenya Police Chief Joseph Boinet said the gunmen forced their way into the university at 5.30am by shooting at the guards manning the main gate.

It is not clear if any of the students the militants said they were holding were alive at the time of the final assault.

However, officials said more than 500 students had been rescued.

Authorities have offered a $215,000 (£145,000) reward for a man called Mohammed Mohamud, who has been identified as a possible mastermind of the attack.

Collins Wetangula, the vice chairman of the student union, said he was preparing to take a shower when he heard gunshots coming from a dorm.

"All I could hear were footsteps and gunshots; nobody was screaming because they thought this would lead the gunmen to know where they are," he said.

"The gunmen were saying sisi ni al-Shabab (Swahili for we are al-Shabab).

"If you were a Christian you were shot on the spot.

"With each blast of the gun I thought I was going to die."

Grace Kai, a student at a neighbouring college, said there had been warnings of an imminent attack.

"Then on Monday our college principal told us ... that strangers had been spotted in our college.

"On Tuesday we were released to go home, and our college closed, but the campus remained in session, and now they have been attacked."

Kenya's northern and eastern regions, which border Somalia, have been most affected by attacks blamed on al Shabaab Islamists.

The militants, who have links to al Qaeda, have vowed to take retribution against Kenya for sending its troops to Somalia.

Al Shabaab was responsible for the deadly attack in 2013 on the Westgate shopping mall.

The US said it condemned the latest attack in the "strongest terms", while the British government pledged to continue to support Kenya in the country's battle against terrorism.