The Syrian Democratic Forces (SDF) on Thursday (June 22nd) succeeded in surrounding the "Islamic State of Iraq and Syria" (ISIS) stronghold of al-Raqa city.

They have now closed the southern flank -- the last open area, south of the Euphrates River -- according to the Syrian Observatory for Human Rights.

A section of this approach to the city is now under the total control of the Arab-Kurd alliance, while the remaining section is in range of their direct fire.

The SDF on Thursday seized control of the Kassarat area south of al-Raqa and reached the new bridge, thus completing the siege on four sides.

The other three sides were already under SDF control.

The SDF are carrying out "precise, sensitive and lengthy military operations in the city of al-Raqa, with the aim of eliminating the terrorists", SDF spokesman Brig. Gen. Talal Sello said Thursday.

The liberating forces are trying to protect civilian lives, he added, noting that ISIS fighters have been using some of them as human shields.

Sello called on al-Raqa residents to stay away from ISIS positions for their own safety and to avoid potential harm from the intensifying clashes.

With international coalition support, SDF fighters were able to encircle al-Raqa city almost entirely, after closing in on it from all four sides, SDF unit commander Ghassan Ibrahim told Diyaruna.

They most recently advanced along the southern flank after capturing al-Talaaeh camp area, he said.

The Kassarat area, including Kasrat Sheikh Jumaa and Kasrat al-Faraj, is now also under SDF control, Ibrahim said, adding that "the new bridge area has fallen militarily as it is in the range of SDF machine guns and direct weapons".

Closer to city centre

Some sections of al-Raqa city itself are under full SDF control, Ibrahim said, describing the current situation as "excellent".

In the eastern section of the city, the SDF has been pushing in on al-Rumaila and al-Rawda districts.

"The pace of the advance has slowed, because the SDF are getting closer to the city centre, and the battle has turned into street warfare," he said.

"This is one of the most difficult types of warfare, and is made more so as ISIS is using thousands of civilians as human shields in an attempt to slow the advance of the liberating forces and find ways to escape from the city," he said.

As the SDF advances, he said, its fighters must be on the lookout for the tunnels ISIS dug underground, as well as aboveground passageways it created by opening holes in walls to allow movement from house to house.

They also must exercise caution as ISIS has planted hundreds of mines and improvised explosive devices (IEDs) in most streets and houses, Ibrahim said.