GARISSA, Kenya, April 2 -- At least 15 people have been confirmed dead and 65 others injured after gunmen stormed a university in northeast Kenya early Thursday.

Kenya's Majority Leader of National Assemby Adan Duale confirmed the death toll, saying major security operation was still underway to rescue more students who were still trapped inside the university.

"Death toll has risen to 15, and we have 65 people injured," said Duale, who is at the scene with senior government and security officials.

Somali militant group Al-Shabaab has reportedly claimed responsibility for the attack.

"We have killed many people and Kenyans will be shocked when they get inside," they said in their radio station.

Internal security ministry said the Moi University campus in Garissa has been secured and attacks cornered as rescue mission continues. The ministry said three out of four hostels have been evacuated as attackers are in one hostel.

The heavily armed assailants forced their way into the university at about 5:30 a.m. local time and gained entry into student hostels after firing at guards manning the main gate.

Kenya Red Cross Society (KRCS) said the attack was preceded by an explosion at the university's gate. The number of student hostages is unknown, but 50 of them have been safely freed, it said.

The organisation said it is leading a medical evacuation and working with the health ministry to deploy surgeons to the grounds. It said it is evacuating casualties to the Garissa Provincial General Hospital where it is organising a blood donation drive with the ministry.

The team is further organising for the severely injured to be airlifted to Nairobi and has set up a psychological support desk for victims and families.

Witnesses say the gunmen went into the university as students were going for morning prayers. Those calling from inside the university say there are many casualties.

The attack comes after three universities had issued security alerts barely a week before the latest attacks, informing students and staff of new security measures while cautioning people within their campuses to be extra vigilant.

Kenyatta University, the University of Nairobi, and the United StatesInternational University in the capital Nairobi had warned the students there was credible intelligence of possible terrorist attacks of a university or college in Kenya.

"Intelligence reports indicate that the Al-Shabaab terror group is planning retaliatory attacks on vital installations in Nairobi, including a major university," the University of Nairobi Chief Security Officer W.M. Wahome said in its memos to students dated on March 25.