Kenya's military has launched air strikes against al-Shabab bases in Somalia following an attack on a Kenyan university that killed 148 people.

Colonel David Obonyo, a military spokesman, said on Monday that warplanes had attacked positions of the al-Shabab group on Sunday afternoon and early Monday morning.

Al-Shabab, which is based in Somalia, claimed responsibility for Thursday's attack on the Garissa University College campus in northeastern Kenya.

After besieging the university, the al-Shabab gunmen lined up non-Muslim students before executing them in the armed group's bloodiest attack to date.

The attack claimed the lives of 142 students, three police officers and three soldiers.

President Uhuru Kenyatta on Saturday pledged that the attackers would face justice for the "mindless slaughter" and vowed to retaliate for the killings in the "severest way".

Previous strikes

Monday's air strikes were not the first launched by Kenya against al-Shabab targets.

In June last year, Kenyan fighter jets attacked two bases belonging to al-Shabab fighters in Somalia, killing at least 80 of them, according to African Union (AU) peacekeeping troops deployed there.

Kenyans worry about radicalisation after Garissa attack

The African Union Mission in Somalia (AMISOM), whose soldiers launched a new offensive against al-Shabab last year, said the Kenyan jets carried out the raids on Anole and Kuday in Somalia's southern Lower Jubba region.

Kenya first sent its troops into neighbouring Somalia in 2011 after several attacks inside its territory that it blamed on al-Shabab. It later joined the AMISOM peacekeeping force.

Al-Shabab has since carried out a string of attacks to punish Kenya for its intervention, including a raid on Nairobi's Westgate shopping mall in September 2013 that killed at least 67 people.

Kenya responded the following November by "completely destroying" an al-Shabab training camp about 300km west of the Somali capital Mogadishu, which was believed to have housed more than 300 al-Shabab recruits.

Source: Al Jazeera and agencies