Washington DC - The State Department warned on Monday of a threat to US facilities and schools in Nigeria, urging Americans to take precautions.

"The US embassy in Abuja informs US citizens of a possible terrorist threat against US facilities and US affiliated schools in Nigeria," it said in a notice.

"Increasing awareness of your surroundings, avoiding predictable routines, and reviewing general security precautions with your family can help reduce your risk," it said.

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The embassy did not spell out the source of the threat.

President Donald Trump on Christmas Day ordered US bombings of Nigeria, saying he was targeting jihadists.

The attack came after Trump complained that Christians were facing persecution in Africa's most populous nation, an assessment that is contested in a country that has seen widespread violence against both Christians and Muslims.

The warning in Nigeria also comes amid a global security warning by the US after Washington and Israel attacked Iran, which has responded with missile and drone attacks against its US-aligned neighbors.