It is the Muslim holy month of Ramadan but the US State Department has warned its citizens at home and abroad to be alert as an increased risk of terror attacks by the ISIS loom on them.

The alert was issued in response to an audio message by ISIS spokesperson Abu Mohammad al-Adnani. In the audio clip, Adnani urged all extremists to “get prepared, be ready … to make it a month of calamity everywhere for nonbelievers … especially for the fighters and supporters of the caliphate in Europe and America.”

A report by the State Department-led Overseas Security Advisory Council said that the fact that there were three deadly attacks after a similar message was sent out by Adnani last year made the recent one more credible, the Independent reported.

“According to Islamic practice, sacrifice during Ramadan can be considered more valuable than that made at other times, so a call to martyrdom during the month may hold a special allure to some,” the report said.

A couple of weeks ago, Adnani had urged its followers to launch attacks in their own cities if they are unable to reach Iraq and or Syria. “The tiniest action you do in the heart of their land is dearer to us than the biggest action by us,” the audio message said. “There are no innocents in the heart of the lands of the Crusaders.”

Ramadan began earlier this week and is a holy month during which fasting and other sacred ceremonies are observed. For ISIS, Ramadan began by burning 19 Yazidi girls alive for refusing to become sex slaves.

“The 19 girls were burned to death while hundreds of people were watching. Nobody could do anything to save them from the brutal punishment,” the NDTV quoted a witness as saying. The ISIS abducted over 3,000 Yazidi girls in 2014 after invading Sinjar, located to the northwest of Iraq.