An American Muslim advocacy group has called for an FBI bias investigation after a gunshot was fired through the dome of an Illinois mosque Tuesday morning. Bias crime is a category that covers hate crimes.

“It happened during morning prayers when there were people inside,” Ahmed Rehab, executive director at the Council on American-Islamic Relations (CAIR)-Chicago, told Al Jazeera. “It disrupted the prayer and debris fell down from the dome onto people.”

There were about 40 worshipers in the Prayer Center at Orland Park (OPPC) in Orland Park, Ill. at 6:05 a.m. when the shot was fired, CAIR said in a news release. No injuries were reported.

Orland Park police confirmed that there was "criminal damage" at the mosque, and said the incident is being investigated.

“Someone put a round through the dome,” Sgt. Scott Malmborg of the Orland Park Police Department told Al Jazeera. He said the shooting is not being investigated as a bias crime – the category that covers hate crimes – because intent has not yet been established.

But CAIR’s Chicago office has issued a statement calling for an FBI bias probe into the incident.

Meanwhile, prayers will continue to be held at their regular times at the mosque, Rehab said.

This is not the first time a shot has been fired into a mosque in the United States this month. Last week, CAIR called for a bias probe into a separate shooting at a mosque in Mississippi.

On March 18, several shots were fired into doors, windows, and walls of the Islamic Center of Hattiesburg in Hattiesburg, Miss. Police investigated the incident as a "malicious mischief case," according to local media reports.

"Incidents such as this have a chilling effect on worshipers. No one should have to go to their place of worship worried if they'll make it back home alive," Rehab said in the CAIR news release.