The number of deadly attacks by Islamic extremists is mounting across Africa, raising questions about the resurgence of armed groups once seen to be in decline. Here is a brief description of the attacks and an explanation of who was behind them and what is driving the surge.

RECENT ATTACKS

— On Jan. 21, al-Shabab fighters stormed and took over a beachfront restaurant in Somalia's capital, Mogadishu. When the siege was over, more than 20 people had been killed in the attack.

— On Jan. 15, gunmen stormed a cafe popular with foreigners in Burkina Faso's capital, firing at people, setting the cafe ablaze and then attacking a nearby hotel. At least 30 people were killed after a more than 12-hour siege. The North Africa branch of al-Qaida, al-Qaida in the Islamic Maghreb, claimed responsibility.

— On Jan. 15, al-Shabab attacked an African Union base in Somalia, killing an unknown number of Kenyan peacekeepers. Al-Shabab claimed it had killed about 100 Kenyans. Kenyan authorities have not given a death toll. Kenya has provided a major contingent to the African Union force that is fighting al-Shabab and assisting the elected government of Somalia.

— On Dec. 28, Boko Haram Islamic extremists struck a city and a town in northeastern Nigeria with rocket-propelled grenades and multiple suicide bombers, killing at least 80 people in Maiduguri, a state capital.

— On Nov. 20, Islamic extremists seized dozens of hostages at the Radisson Blu hotel in Mali's capital, Bamako. At least 20 people were killed along with two gunmen during the more than seven-hour siege. Al-Qaida in the Islamic Maghreb and al-Mourabitoun said it was their first joint attack since al-Mourabitoun joined AQIM.

THE JIHADIST GROUPS

— Al-Shabab, which wants to overthrow Somalia's weak, U.N.-backed government, counts veterans from the Iraq, Afghanistan and Pakistan conflicts among its ranks. Fighters also include young men recruited from Somali communities in the U.S. The group is not as strong as it once was but still has the capacity to carry out deadly attacks within Somalia and across borders. Al-Shabab is linked to al-Qaida, though some members have reportedly sworn allegiance to Islamic State, creating friction.

— Al-Qaida in the Islamic Maghreb, or AQIM, expanded from Algeria south into Mali under pressure from Algerian security forces in the early 2000s, recruiting disaffected Malians and Mauritanians. It made a fortune in smuggling and in ransoming hostages under militant Moktar Belmoktar. He split off to form the Masked Brigade in 2012, which in August 2013 merged with another group to create al-Mourabitoun (The Sentinels). AQIM announced in December al-Mourabitoun had joined its ranks.

— Boko Haram, the Nigerian Islamic extremist group, emerged as much more radical entity after security forces attacked its compound in Maiduguri in 2009, killing 700 people. Boko Haram pledged allegiance to the Islamic State group last year.

ATTACKS: WHY NOW?

"This is the result of a combination of factors, including competition between extremist groups for attention and, ultimately, recruits and resources, as well as opportunity," said J. Peter Pham, director of Atlantic Council's Africa Center, talking about the rise in extremist attacks.

Somalia's government, which relies on troops from African countries for security, has called for sustained internal help in dealing with Islamic extremists. The government has also tried to offer amnesty to al-Shabab fighters in hopes they will renounce violence.

In West Africa, following the attack in Burkina Faso, "the specter of terrorism now hovers over much of the region," according the Verisk Maplecroft, a group of risk analysts. It said that attack signifies a shift from extremist groups in the Sahel region targeting U.N. and foreign military personnel to attacking civilians as well.