Kenyan warplanes bombed militant camps in Somalia, officials said Monday, following a vow by President Uhuru Kenyatta to respond “in the fiercest way possible” to a massacre of college students by al-Shabab extremists.

The airstrikes Sunday and Monday targeted the Gedo region of western Somalia, directly across the border from Kenya, said Col. David Obonyo of the Kenyan military.

The al-Shabab camps, which were used to store arms and for logistical support, were destroyed, but it was not possible to determine the number of casualties because of poor visibility, he said.

The Somalia-based militant group claimed responsibility for Thursday’s attack at Garissa University College that killed 148 people, most of them students.

The extremist group said the Garissa attack was in reprisal for Kenya sending troops into Somalia in 2011 to kill its members who took part in cross-border raids and kidnappings.

Kenya’s troops in Somalia are part of an African Union force and are also shoring up the beleaguered Somali government. Kenya has conducted airstrikes in Somalia before.

The four al-Shabab attackers who stormed the university were killed by Kenyan security forces, and their bullet-riddled bodies were displayed in Garissa. Five people have been arrested on suspicion of involvement in the attack, a Kenyan official said.

The al-Shabab group has struck several times on Kenyan soil, although last week’s assault was the deadliest. Other attacks have occurred elsewhere in northeastern Kenya last year, as well as at the upscale Westgate shopping mall in the capital of Nairobi in which 67 people died in 2013.

The group pledged to strike again against Kenya, saying: “No amount of precaution or safety measures will be able to guarantee your safety, thwart another attack or prevent another bloodbath.”

In a nationally televised address over the weekend, Kenyatta vowed that his administration would retaliate against the extremists.

“We will fight terrorism to the end,” he said. “I guarantee that my administration shall respond in the fiercest way possible.”

Kenyatta has been under pressure from the political opposition to deal with the security threat from the Islamic extremists. In December, he finally fired the interior minister, who was ridiculed for a slow response to the Westgate attack, and accepted the resignation of the national police chief.

A leading member of parliament, Aden Duale, said Monday that work must be done to prevent Kenyan youths from becoming followers of extremism.

“Some of our youth have fallen victim to this evil ideology of al-Shabab,” he said. “We will embark on an immediate, massive and sustained campaign to win back the hearts and the minds of our youth within our constituencies and the countries as whole. We recognize that some of our religious institutions have had some role in radicalization and propagation of this ideology.”