A wave of violence from Islamist militant groups left at least 19 dead in Nigeria and the surrounding area over the weekend, highlighting the limits of a concerted months-long Nigerian-led counterinsurgency effort.
The two attacks on Friday and Sunday were reportedly carried out by the Islamic State and Boko Haram.
On Friday, suicide bombers carried out two attacks in Nigeria's capital of Abuja, killing at least 15 people. Nigeria's President Muhammadu Buhari initially blamed the attack on Boko Haram, but the Islamic State later claimed responsibility on Twitter on Sunday.
The authenticity of the group's statement, which did not mention Boko Haram and was issued under the name Islamic State West Africa, could not be immediately verified.
Then on Sunday, suspected Boko Haram militants from Nigeria killed three civilians and a soldier in a double suicide attack across the border in Niger, according to security sources.
In May, the leader of the Islamic State militant group that controls parts of Syria and Iraq accepted a pledge of allegiance from Boko Haram, according to his spokesman. But the extent of cooperation between the two groups remains largely unknown.
Nigeria has been battling a violent insurgency from Boko Haram for the past six years. In the past few months, the fight has spilled over into neighboring Niger, Cameroon and Chad from Boko Haram's strongholds in northern Nigeria.
The Nigerian military, aided by forces from the surrounding region, has expanded its counter-offensive significantly in the past year. Niger has arrested at least 1,100 suspected Boko Haram militants this year and has placed its Diffa region under a state of emergency.
Diffa, which borders Nigeria, has suffered at least 57 attacks since February, statistics published by the United Nations on Friday showed. At least 150,000 refugees seeking protection from Boko Haram attacks now live there.