A Sheffield radio station has been taken off the air after broadcasting 25 hours of lectures "encouraging and condoning" violence towards non-Muslim people.
Ofcom began to investigate Iman FM after a listener complained that they had aired lectures encouraging violence and religious hatred during Ramadan.
Iman FM confirmed that they had broadcast 25 hours worth of lectures by the American Muslim cleric Anwar al-Awlaki.
The regulators concluded that parts of al-Awlaki's lectures amounted to a "direct call to action to members of the Muslim community to prepare for and carry out violent action against non-Muslim people".
Iman FM, a community radio station broadcasting to the Muslim community in Sheffield, said that it had broadcast a series of pre-recorded lectures by al-Awlaki during Ramadan.
Ofcom concluded that they had "serious concerns" about Iman FM's decision to give a platform to a "widely-known terrorist leader an al-Qaeda recruiter".
Al-Awlaki was designated a global terroritst by the US government in 2010 and was placed on the UN Security Council Resolution's list of individuals associated with al-Qaeda in 2011.
His sermons, which Ofcom said overtly endorse violence as a religious duty, are believed to have inspired several recruits to Islamic militancy.
This sparked terrorist attacks including the Charlie Hebdo office attack in Paris in 2015, killing 12 people and the 2009 Ford Hood shooting where 13 US soldiers were killed.
The station broadcasts a live daily breakfast show from 8am to 10am but they were without their regular presenter over the course of the holy month.
As a result, it decided to broadcast a series of pre-recorded lectures focussing "on the life of the Prophet Muhammad" and "lectures on Seerah".
Iman FM accepted that, due to time constraints and the timing falling within the month of Ramadan, they had not fully listened to the recordings prior to broadcast.
During the broadcast, Ofcom decided that the cumulative effect of al-Awlaki's statement would "condone, promote and encourage violent behaviour towards non-Muslim people".
Ofcom said: "Further, the lectures appeared to link violent acts of the past with actions that might potentially be taken today.
"Ofcom took the view that the content therefore amounted to a call to action which was likely to encourage or incite the commission of crime or lead to disorder."
The regulator also found that the lectures contained "hate-speech" towards Jewish people as al-Awlaki refers to the Prophet Muhammad's "alleged order to kill a Jewish opponent".
Ofcom said: "In our view this statement would have been interpreted justifying a “negative attitude” and critical view towards Jewish people, based on what it termed that community’s “mindset” and their “evil actions”.
"We considered this statement would have been perceived by listeners as justifying hatred or violence towards Jewish people, and therefore is a clear example of hate speech as defined by the Code."
Al-Awlaki was killed in a drone strike in Yemen, authorised by President Obama, but his writings and sermons remain available online.
Iman FM said it was “not aware of the background of the preacher and had no knowledge of him being proscribed by the United Nations”.
It added that “had this fact been known” they would not have broadcast the lectures and accepted the material breached the broadcasting code.
Iman FM have now removed the lectures from the air and would run dilligence checks in future on the background of speakers before broadcasting their speeches and lectures.
A statement on Iman FM's Facebook page read: "This is to inform you that IMAN FM has temporarily stopped broadcasting, this has resulted due to the regulator suspending its licence for the next 21 days, on the basis that unwittingly some controversial lectures were broadcast.
"Please note that we are trying our level best to remedy this situation and look forward to broadcasting as soon as possible.
"We thank you for your continued support in the mean time. IMAN FM Management"