US-backed Syrian rebels gain on IS in Raqqa

US-backed Syrian rebels gained ground against the Islamic State group in the streets of Raqqa on Wednesday, a day after their months-long offensive finally pierced into the militant group's Syrian stronghold.

The Syrian Democratic Forces - a militia made up of Arab and Kurdish fighters - has=ve spent seven months advancing on the city with aerial backing from the US-led coalition.

On Tuesday, SDF fighters finally broke into Raqqa's eastern al-Meshleb district. This progress was followed by the capture of the neighbourhood and the Harqal citadel to the west of the city on Wednesday morning, the command of Operation Wrath of the Euphrates said.

The citadel is situated on a hilltop just two kilometers from the city limits.

According to the Syrian Observatory for Human Rights, fighting also took place at a military complex roughly two kilometers north of the city.

The monitoring group the advance was preceded by bombing by the international anti-IS coalition.

One of Tuesday's airstrikes inside the city killed eight civilians, including three children, Observatory head Rami Abdel Rahman told AFP.

After Raqqa was captured by IS in 2014, the city became notorious for the group's execcutions, public beheadings and displays of victims' bodies. 

It is also thought that the city became a hub for planning the extremist group's attacks abroad.

Around 300,000 civilians were believed to have been living under IS rule in Raqqa, including 80,000 displaced from other parts of Syria.

In recent months, thousands have fled the intensification of fighting and US-led airstrikes that have claimed civilian lives.

The UN humanitarian office said Tuesday that about 160,000 still remain in the northern city.