At least 300 people have been killed in more than 20 attacks that the al-Shabab group has carried out in Kenya in the last five years.
Based in the horn of Africa, the al-Qaeda-linked group initially concentrated its attacks in Somalia, where it wants to impose a strict version of Islamic law and is fighting to overthrow the western-backed government.
But since 2011, the armed group has increasingly targeted Kenya.
In 2013, it claimed responsibility for a deadly mall attack in Nairobi that killed more than 60 people. In April 2015, an attack on a university in the town of Garissa left at least 147 dead.
In 2011, following a spate of kidnappings in its coastal region, Kenya sent its troops into neighbouring Somalia to target al-Shabab fighters which it blamed for the abductions which al-Shabab denied involvement in.
Kenyan troops, backed by Somali soldiers, pushed al-Shabab out of several towns the group controlled in southern Somalia.
The armed group then started carrying out deadly attacks in Kenya, saying they were in retaliation to Kenyan troops crossing into Somalia.
“They invaded the Muslim land of Somalia … it’s our duty to take revenge,” al-Shabab’s spokesperson Sheikh Ali Dheere had told Al Jazeera in 2014 after the group killed 28 people in an attack in Mandera.
The group has also claimed responsibility for attacks in Djibouti and Uganda – two countries whose troops are part of a UN-mandated African Union peacekeeping mission in Somalia fighting al-Shabab.
A 2010 twin bombing by the group in Kampala left at least 70 dead. Four years later, a suicide attack at a restaurant in Djibouti killed three people.
Burundi and Ethiopia have also contributed troops to the AU mission in Somalia but have not suffered attacks by the armed group.
Kenya has a land border with Somalia of more than 600km. Most of the armed group’s attacks happened near this porous border as the fighters are able to cross over easily.
The communities living in this region – northern and coastal area – have long felt abandoned by the central government in Nairobi.