The United States government has issued a worldwide travel alert for American citizens, saying they should be ‘extra cautious’ following the Sydney Martin Place siege.

In the alert issued over the weekend, the Bureau of Consular Affairs said the “lone wolf attack in Sydney” was a “reminder that U.S. citizens should be extra cautious” and “maintain a very high level of vigilance”.

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The worldwide travel alert is only the second of its kind, with the first one issued in August 2013 after the government had evidence of a potential Al Qaeda attack.

The latest report warns attacks will no longer happen just on government buildings, but on hotels and places of worship.

“An analysis of past attacks and threat reporting strongly suggests a focus by terrorists not only on the targeting of U.S. government facilities but also on hotels, shopping areas, places of worship, and schools, among other targets, during or coinciding with this holiday period.”