The US embassy in Nigeria warned on Sunday of a possible attack against diplomatic missions in Lagos, the commercial capital of Africa's biggest oil producer.
In a message to US citizens living in Nigeria, the embassy said it had received reports of a possible strike against missions located close to the US Consulate General in Lagos, situated in the exclusive Victoria Island neighbourhood.
"US Mission Nigeria has received reports about a possible attacks against diplomatic missions in Lagos located on Walter Carrington Crescent," the message said.
It said the Nigerian police had increased their vigilance in the neighbourhood and called on U.S. citizens to report any suspicious activity.
Nigeria, the world's eighth biggest exporter of crude oil which supplies the United States and China, has never been the victim of a major terrorist attack. But militants in the southern Niger Delta, the heartland of its oil industry, have carried out regular strikes against installations belonging to oil giants including US firms.
The US embassy message gave no details of the nature of the reports it had received regarding the possible attack in Nigeria, Africa's most populous nation divided roughly equally between Christians and Muslims.
But it noted that US government facilities worldwide remained in a state of heightened alert because of "the continuing threat of terrorist actions and violence against Americans and US interests".