NAIROBI, Kenya (AP) — A Kenya police official says South Sudanese security agents have arrested three Kenyans and a Somali refugee for allegedly attempting to go to Libya to join the Islamic State extremist group.

Kenya police spokesman George Kinoti said Tuesday the families of the four men assisted authorities with information that led to their apprehension in South Sudan on Thursday. They were returned to Kenya on Sunday.

Kenya is attempting to stem the recruitment of youths to extremist groups. Hundreds of young Kenyans are reportedly the largest contingent of foreign fighters in Somalia’s deadly al-Shabab extremist group, which is allied to al-Qaida. Al- Shabab has carried out more than 100 attacks on Kenya and said the violence is retribution for Kenya sending troops to Somalia to fight the group.