Islamic State (Isis) militants in Syria have reportedly issued a circular banning residents of Raqqa from holding public gathering for Eid al-Fitr celebrations over fears that the Assad forces are planning to launch an air attack on the city on the day of Eid.

Syrian underground media activist group - Raqqa is Being Slaughters Silently (RBSS) - has reported on its social media accounts that people have been asked to avoid public celebrations during Eid al-Fitr.

Isis also reportedly has placed concrete blocks filled with oil across the city and residents have been asked to light them up during an air raid. 

Recently, Isis had issued a similar ban, asking rseidents of Mosul to avoid Eid al-Fitr celebrations and prayers on the ground that such customs were not part of 'early Islam' during Prophet Mohammed's time.

[Also Read: Isis Marks Eid al-Fitr; Releases Execution Video Showing Child Fighter Beheading Syrian Army Captain ]

In recent months, Raqqa, which is the de facto capital of the Islamist radical group, has faced heavy casualties.

In June, the Kurdish militia, YPG, assisted by US-led coalition airstrikes, killed many Isis militants near Raqqa and captured several border towns from the group. 

The U.S. Central Command on Thursday issued a statement that it conducted 15 air raids near five Syrian cities, including five near Raqqa and four near Hasaka, on 15 July.