Blasts and sirens rang out over Bahrain and authorities urged residents to seek shelter on Sunday as Iran's Guards said they had attacked a US military base in the Gulf nation.
Alarm sirens blared, according to an AFP journalist, while authorities posted several alerts on social media, without specifying the source of the threat.
The interior ministry in an X post urged "residents to remain calm, proceed to the nearest safe location, and follow news through official channels for the protection of public safety".
Explosions could be heard around 4:00 am (0100 GMT), the AFP journalist said, with residents reporting a second series of blasts around 6:30 am (0330 GMT).
Iran's Revolutionary Guards said their forces carried out a drone attack on a US radar system at a base in Bahrain, according to a statement carried by the Iranian state broadcaster on Sunday.
"The US air defense radar system at the Al-Riffa helicopter base in Bahrain was targeted by six drones belonging to the IRGC Aerospace Force," the Guards said in a statement posted by the state broadcaster on Telegram.
"The Strait of Hormuz is closed, and any aggression by the American enemy will be met with an even harsher and more forceful response," it added.