The US embassy has issued an official warning to its citizens to be ‘highly vigilant’ of potential terrorist threats when visiting Australia.

This is reportedly the first time such a warning has been issued by the embassy this century.

“US citizens are reminded to be aware of your surroundings during this time of heightened alert, and report to authorities any suspicious individuals or items you may see,” said an alert on the embassy’s website.

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Americans were “strongly encouraged” to monitor local news for updates and “maintain a high level of vigilance”.

“Maintain a high level of vigilance and take appropriate steps to enhance your personal security,” the alert said.

Australia’s risk of a terror attack was lifted to ‘likely’ last year by the Abbott government after a series of raids.

In April, a teenager was arrested on suspicion of plotting an attack to be carried out on Mother’s Day, which the embassy referenced in its alert.

The embassy warned that the arrested individual allegedly had the “intent to conduct terrorist attacks against members of the general public”.