Kenya launched airstrikes against fighters from the armed group Al-Shabab in Somalia after an attack on Garissa University College in eastern Kenya that killed 148 people, a military spokesman said Monday.

In the first major military response to last week's attack, warplanes attacked two camps of Al-Shabab on Sunday afternoon and early Monday morning, said Col. David Obonyo of the Kenyan military.

Al-Shabab, which is based in Somalia, claimed responsibility for the April 2 attack in the Kenyan town of Garissa. Four gunmen died in the assault, which ended after a 15-hour siege. The group has killed more than 400 people in Kenya since April 2013.

The airstrikes occurred in the Gedo region of Somalia, Obonyo said. "This is part of continuing operations, not just in response to Garissa," he said.

Jets pounded the camps in Gondodowe and Ismail, near the border with Kenya. Cloud cover made it difficult to establish how much damage the bombings caused or to estimate the death toll.

Kenyan President Uhuru Kenyatta had vowed harsh measures against Al-Shabab after the attack on Garissa, which is near the border with Somalia. Kenya has troops in Somalia as part of an African Union force to attack Al-Shabab and shore up the beleaguered Somali government. Kenya has carried out airstrikes before, but it has struggled to stop the flow of Al-Shabab militants and weapons across its porous border with Somalia.

Al-Shabab said it attacked students at Garissa University College in reprisal for Kenya’s sending troops into Somalia. Nairobi decided in 2011 to provide troops to the African Union Mission in Somalia (AMISOM), with United Nations approval. The peacekeeping mission — which includes a military component that draws troops from Ethiopia, Djibouti, Burundi, Sierra Leone and Uganda — was put together to root out Al-Shabab from its strongholds in southern and central Somalia. The mission has counted a number of significant successes in recent years, such as the recapturing of important port cities along the Somali coast and the killing of several Al-Shabab leaders.

In March, AMISOM seized Kuday, an island off the port city of Kismayo that Al-Shabab fighters used to smuggle contraband charcoal that it sells to Gulf states to sustain its operations. The killing that month of Adnan Garaar, who allegedly helped plan the attack at the Westgate mall in Nairobi, by a U.S. drone also delivered an important blow to the organization, the Pentagon reported. Much of the capital, Mogadishu, is back in the Somali government’s hands, AMISOM reported, but car bombs and suicide attacks continue to rock the city.

Al-Shabab, Somalia's largest armed group, started out as one of many factions fighting the U.N.-backed transitional federal government, based in Mogadishu. Al-Shabab morphed into what the United States labeled a terrorist organization after staging attacks on prominent foreign and national targets.

Al Jazeera and wire services