It said the threat pertains to the upcoming 2019 general elections.
Full statement below:
There is an increase in ISIS propaganda videos specifically directed to Nigeria and the ongoing civil unrest in Borno state and the Northeast. ISIS West Africa (ISWA) and Boko Haram have both stated they plan to disrupt the upcoming 2019 presidential elections by conducting attacks on Nigerian Security and infrastructure, as well as places of gathering such as markets, hotels, and malls.
While we have no specific threat information to the U.S. Embassy or within Nigeria during the election season, U.S. citizens in Nigeria should remember to follow personal security precautions on a regular basis.
Actions to Take:
Expect additional police and military checkpoints and possible road blocks throughout the country
Carry proper identification, including a U.S. passport with a current Nigerian visa, if needed
Exercise caution when walking or driving at night
Review travel routes and times to reduce time and place predictability
Avoid crowds and demonstrations.
Be aware of your surroundings
Keep a low profile
Stay alert in public places, including schools, hospitals, government facilities, places of worship, tourist locations, and transportation hubs
Review your personal security plans
Monitor local media for updates.