The US is warning all of its nationals who are or are planning to travel abroad of an increased threat to their safety from extremist groups.

The US is warning all of its nationals who are or are planning to travel abroad of an increased threat to their safety from extremist groups.

The rare worldwide travel warning cites "current information" indicating that the so-called 'Islamic State of Iraq and the Levant' (ISIL), al-Qaeda and Nigeria’s Boko Haram terrorist groups are plotting to target US nationals in multiple regions.

"These attacks may employ a wide variety of tactics, using conventional and non-conventional weapons and targeting both official and private interests," the State Department said in the written alert.

The department warned that the return of ISIL terrorists to their home countries from Iraq and Syria will increase the likelihood of terror attacks, while terrorists continue to be a threat.

The warning follows a series of attacks claimed by ISIL that have killed or maimed hundreds in Beirut and Paris. The extremist group also claimed the downing of a Russian plane that departed from Egypt’s Sharm el-Sheikh, killing all 224 on board.

The travel alert will expire at the end of February.