The United States Government has released a global security alert for its citizens in Nigeria and across the world following rising tensions between Washington and Tehran.

The advisory, issued by the State Department on Sunday, called on Americans to remain vigilant in the wake of recent US military operations targeting Iran.

According to the notice, shifting security developments could disrupt travel plans and pose safety concerns, including possible interruptions to air travel.

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"Following the launch of U.S. combat operations in Iran, Americans worldwide and especially in the Middle East should follow the guidance in the latest security alerts issued by the nearest U.S. embassy or consulate," the advisory reads.

"They may experience travel disruptions due to periodic airspace closures. The Department of State advises Americans worldwide to exercise increased caution."

The alert further advised US nationals to sign up for the Smart Traveler Enrollment Program (STEP) to receive up-to-date security information.

It also encouraged citizens to monitor the "U.S. Department of State Security Updates for US Citizens" WhatsApp channel for additional updates.

The warning follows coordinated strikes carried out by US and Israeli forces on Iranian targets. The attacks reportedly resulted in the deaths of Iran's supreme leader Ayatollah Ali Khamenei and chief of staff of the armed forces, Abdolrahim Mousavi.

Iranian authorities and regional observers estimate that the strikes have left more than 200 people dead and over 700 others injured.

Several senior commanders of Iran's Islamic Revolutionary Guard Corps, along with other defence officials, were also said to have been killed.

In the wake of the attacks, President Donald Trump stated that Iran's leadership had agreed to return to negotiations with the United States after the bombardments of multiple Iranian cities.

Trump said Tehran initiated contact for talks and that he had agreed to the proposal.