Kenya’s President Uhuru Kenyatta confirmed that hostages were taken in the deadly attack on a university in Garissa early Thursday and urged Kenyan officials to speed up the recruitment of thousands of new police officers. “I am saddened to inform the nation that early today, terrorists attacked Garissa University College, killed and wounded several people and have taken others hostage,” Uhuru said in a brief state of the nation address, adding that further details would come “in due course.”

Kenyatta did not outline how Kenyan security officials would prevent future terror attacks, but he called on police “to take urgent steps and ensure that the 10,000 recruits whose enrollment is pending” be accelerated, according to Reuters.

Al-Shabab militants claimed responsibility for the pre-dawn assault, which left at least 15 people dead and at least 65 others wounded. A spokesman for the Somalia-based terror group said Christians were taken hostage but didn’t specify a number, according to Agence France-Presse.

“When our men arrived, they released the Muslims. We are holding others hostage,” al-Shabab spokesman Sheikh Ali Mohamud Rage told AFP. “Our people are still there, they are fighting, and their mission is to kill those who are against the Shabab.”

The United States condemned Thursday’s attack, calling it a show of cowardice. “We are saddened & angered by today’s terrorist attack @ #Garissa Univ. Our deepest condolences 2 family/friends of victims. #CowardsNeverWin,” the U.S. embassy in Nairobi posted on its official Twitter account.

Kenyan Interior Minister Joseph Nkaissery said Thursday one suspect was arrested while attempting to flee the scene of the attack in northeast Kenya. The Kenya National Disaster Operation Center said the whereabouts of 535 of Garissa University College’s 815 students are still unknown, according to the Associated Press.

One survivor of the assault said he saw five gunmen storm the college compound. The alleged al-Shabab militants are believed to be holding an unknown number of Garissa University College students in a dormitory. “Most of the people still inside there are girls,” Michael Bwana, a 20-year-old student who escaped, told AP Thursday.

Al-Shabab pledged loyalty to the al Qaeda terrorist organization in 2012, and the militant Islamist group wants to run Somalia by its own harsh enforcement of Sharia law. The United States, the United Kingdom, the United Arab Emirates, Canada and Australia have designated al Shabab as a terrorist organization.