Islamic State terrorists have reportedly forbidden civilians from fleeing Syria’s Raqqa, which the Kurdish forces are said to be preparing to recapture, Sputnik agency’s sources said. Militants have allegedly begun removing their own families from the stronghold.

The report, citing sources on the ground, follows a US-led coalition’s air propaganda campaign urging citizens to leave the city, which has served as an Islamic State (IS, ISIS/ISIL) stronghold since 2013.

“The time you have been waiting for has come, the time to leave Raqqa,” reads the flyer posted online by Raqqa is Being Slaughtered Silently (RBSS) group, which calls itself a “group of non-violent activists in Raqqa.”

The leaflet depicts three men and a woman with a child escaping a gloomy urban area, leaving ruins and dead militants behind. They are heading to a peaceful landscape with the green hilltops and sun shining through the clouds.

#Raqqa the Coalition drop Leaflets saying "its the time that u wait for long time , its the time to leave the city pic.twitter.com/8uJuN8ebIz — الرقة تذبح بصمت (@Raqqa_SL) 19 мая 2016 г.

"Their [Islamic State] positions used to be clear but since the beginning of the air campaign against them, they've started to resort to hiding among civilians," said Abu Mohammad, an activist with the RBSS.

Despite increased propaganda efforts, US forces denied they are preparing an imminent attack on the city.

“It’s part of our mess-with-them campaign,” source with the US Defense Department told The Daily Beast on Friday.

As the positions of ISIS in Raqqa are getting shakier, the Kurdish militia (YPG) is reportedly looking to attack the city in the coming days, Sputnik reported on Friday, citing a spokesman of the Syrian Democratic Forces (SDF), an alliance of militias fighting terrorist groups in Syria close to the YPG.

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In an interview to the outlet published on Friday, SDF representative Tackir Kobani said the Kurdish-led militia had been discussing the possibility of a dealing a final blow to the terrorists in Raqqa together with the US military.

“Last Tuesday, the leader of the Kurdish Party of Democratic Union, Salih Muslim, and the US special envoy to the coalition against Daesh, Brett McGurk, discussed the strategy to battle Daesh, in particular, for the liberation of Raqqa, Manbij and Jarabulus,” he said, adding that the US-led coalition would back the operation from the air.

“The coalition forces will help us with air support and weapons,” he said.

Earlier, Pentagon rejected Russia’s proposal to conduct joint bombing campaign against ISIS in Syria with Pentagon’s spokesman Navy Captain Jeff Davis saying the US forces does not “not collaborate or coordinate with the Russians on any operations in Syria."

"We are proposing to the US, as the head of the International Syria Support Group, to take part as of May 25 in joint operations between the Russian air force and the air force of the coalition," Russia’s defense minister, Sergey Shoigu, said Friday. The joint air campaign was supposed to target ISIS, Jabhat al-Nusra and other militant groups not included in the US-Russia brokered cession of hostilities agreement as well as “convoys containing weapons and ammunition (and) armed units that illegally cross the Syrian-Turkish border."