Why has the US raised alarms of possible terror attacks in Nigeria’s capital?

Foreign diplomatic missions in Nigeria are sounding alarms over heightened risks of terror attacks in Abuja, the capital city. Security alerts from the US, British, and Australian governments have warned of possible hits on public places including government buildings, shopping malls, hotels, and transport terminals.
“There’s an increased threat of an attack in Abuja. We continue to advise you should reconsider your need to travel to Nigeria,” the Australian foreign affairs travel advisory service said on Oct. 24. “Avoid all non-essential travel or movement,” the US embassy’s statement in Abuja said.