Kenya's interior minister has said security officers ignored intelligence reports prior to the attack on Garissa University College earlier this month.
Joseph Nkaisserry, who is in charge of security, also admitted that the response was poorly co-ordinated.
Militants from the Somali-based Islamist al-Shabab group killed 148 people during the day-long siege at the campus in the north-eastern town.
There has been much public criticism over the alleged security failings.
Correspondents say Mr Nkaisserry's admission is the boldest yet from the government, which has largely been defensive over the terror attack.
Last week, seven top policemen were suspended by Mr Nkaisserry following an initial inquiry into the security failings.
Universities had posted memos warning students of possible violence and the principal of Garissa University College is reported to have requested additional security at the campus, in vain.
Mr Nkaisserry made the comments before a parliamentary committee on security.
The security force's delay in responding to the university attack was caused by poor co-ordination, he said.
The structural design of the campus had also hampered the rescue mission as the accommodation hostels were "like cells as the windows had grills".
The majority of those killed could have been rescued had security officers accessed the college building where they were cornered by terrorists in the morning, he said.
The BBC's Odhiambo Joseph in the capital, Nairobi, says there was drama during the hearing when the minister became involved in a heated exchange with MP Ababu Namwamba.
Another legislator, Zakayo Cheruiyot, then walked out - signalling his dissatisfaction with Mr Nkaisserry's response over the handling of the Garissa attack.
Most of those who died in the raid were students and the attackers singled out Christians to be killed and spared Muslims.
It was worst attack to date in Kenya by al-Shabab, which is affiliated to al-Qaeda.