AMMAN: US-backed forces are “one kilometer” away from cutting off Raqqa city to the south and imposing a full siege on the Islamic State’s capital in Syria, SDF sources on the ground told Syria Direct on Thursday.

Following several days of steady advances south of Raqqa city by the Syrian Democratic Forces (SDF), in addition to heavy overnight battles, “our forces have advanced and just one kilometer” remains to complete the encirclement of the desert provincial capital, an SDF commander told Syria Direct on Thursday.

“The southern front is currently our main focus,” said Rafi, an SDF commander currently in Raqqa city, referring to the southern perimeter.

On Wednesday, SDF forces advanced into and captured the village of al-Kamb southeast of Raqqa city, the commander and another SDF-affiliated source told Syria Direct. Official SDF media has not yet confirmed the advance.

After al-Kamb, only one IS-held village remains for SDF forces to capture in order to fully encircle and besiege Raqqa city.

The Syrian Democratic Forces—a multiethnic militia mostly made up of Kurdish and Arab fighters—launched their battle for Raqqa city on June 6, following seven months of advances in the surrounding countryside that left the provincial capital isolated to the west, north and east.

Since then, completing the siege of the city by cutting it off to the south has been a key goal of the campaign. As the SDF captures ground inside Raqqa city, its Manbij Military Council (MMC) has advanced to into the south, pushing eastwards from Tabqa city, 40km away.

Muhammad Abu Adel, the general commander of the MMC’s Northern Sun Battalions, told Syria Direct on Wednesday that the aim of besieging the city is to “leave no way for IS to escape” and force “either a fight to the death, or surrender.”

Supporting the advance is an intense bombing campaign by US-led international coalition warplanes and artillery fire from US marines based near the city.

On Wednesday, the United States Marine Corps (USMC) posted pictures of operations near Raqqa city on its official Twitter account, adding that Marines “have been conducting 24-hour fire support” for the advancing SDF.

A Kurdish spokesman affiliated with the political wing of the SDF’s largest militia—the YPG—told Syria Direct from Raqqa city earlier this week that “artillery is only being used by the American forces” in the current battles. The spokesman, who requested anonymity, declined to comment on why this would be the case.

US-led coalition aircraft are raining airstrikes on Raqqa city, where an estimated 160,000 civilians remain trapped alongside IS fighters. Over the past week, the coalition has reported at least 139 strikes near Raqqa in support of the SDF campaign.

Airwars, an independent monitor that tracks casualties and coalition airstrikes in Syria and Iraq, estimates that between 4,118–6,360 civilians have been killed by US coalition airstrikes since August 2014.

In the first five months of 2017, before the battle for Raqqa city itself began, Airwars tracked a third more civilian casualties in Iraq and Syria than in the entire year of 2016, the monitor’s Alex Hopkins wrote in a recent opinion piece for Switzerland-based Irin News.

The Islamic State said on Wednesday that its fighters had carried out two successful suicide car bomb (SVBIED) attacks against the SDF in Raqqa’s western al-Romaniyah district in concert with a ground assault. IS claimed the attack killed and injured more than 50 SDF fighters, and drone images of the blast circulated online Wednesday.

An Islamic State SVBIED detonates at an SDF position in Raqqa’s al-Romaniyah district on Wednesday.

On Thursday, SDF commander Rafi confirmed to Syria Direct SVBIED attacks on al-Romaniyah district on Wednesday, but called them a “failed attempt” and “an expected response.” He did not comment on the number of casualties from the attack.

The same day as the IS counterattack in al-Romaniyah, video emerged of IS fighters on motorcycles purportedly dragging the bodies of SDF fighters through the streets of Raqqa city.

SVBIEDs, reinforced and bomb-laden vehicles driven by suicide bombers, have been widely used by the Islamic State for years. A key feature of the battle for Iraq’s Mosul, they are now being used against SDF forces in Raqqa as well.

A recent, 40-minute propaganda video circulated online by the Islamic State’s Wilayat Raqqa media branch earlier this week heavily features suicide car bombings, showing several filmed from the air. The video also shows IS fighters targeting the SDF with heavy artillery and an assault on what appears to be a Raqqa countryside outpost.

On Thursday, as SDF fighters move to encircle Raqqa city, the battle for the heart of the self-proclaimed caliphate in Syria enters a new and dangerous stage for the tens of thousands still trapped inside.

In a study of Raqqa airstrike data published earlier this month, monitor Airwars warned that “more civilians are dying in Raqqa even when fewer targets are hit.” Recent months have seen multiple reports of civilians being killed by coalition bombings while trying to flee to the south, crossing the Euphrates River on barges and boats.

After recent SDF advances, fleeing to the south is no longer an option. And while thousands of civilians have been able to leave Raqqa city in other directions, as the battle intensifies and the frontlines draw closer, it will only become more difficult and dangerous to escape.

Even so, a handful of SDF sources Syria Direct spoke to this week expressed optimism and confidence in the future of the battles.

“It is only a matter of time until we announce the full liberation of the city from this organization of darkness,” said SDF commander Rafi.