"The US Mission in Nigeria is issuing this emergency message to inform US citizens of potential threats against US installations during the 4 July holiday week," said a statement posted on the embassy's website.
Nigeria's capital Abuja was hit by fresh violence late on Tuesday, when a blast went off outside a shopping centre popular with both foreigners and locals.
US citizens in Abuja remain barred from visiting places of worship as well as nearby commercial establishments and must return to their homes by midnight, according to the embassy statement.
The Boko Haram Islamist group, responsible for scores of attacks in recent months, has repeatedly attacked churches, typically on Sundays and holidays.
The embassy "is working with the government of Nigeria to implement additional security measures", through the 4 July holiday week, the statement also said.
Last month, Washington designated three Boko Haram leaders as global terrorists, a move it said was aimed to help stem the violence in Nigeria.
Boko Haram, which has previously threatened to strike US interests, has claimed attacks that have killed more than 1 000 people since the middle of 2009.
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