'Remember to protect civilians': UN expresses concerns over tens of thousands trapped in Syria's Raqqa

The United Nations on Wednesday urged those fighting in Syria's Raqqa to remember "obligations to protect civilians," voicing concern over the tens of thousands of people still trapped without access to aid.

An estimated 10,000 to 25,000 people are stuck in the city, the Islamic State group's main stronghold, said UN spokesman Stephane Dujarric, who noted that "exact figures remain difficult to verify due to the situation on the ground."

"Access to Raqqa is not currently possible for the UN, due to the fighting on the ground," Dujarric said during his daily briefing.

"We remind all military actors of their obligations to protect civilians and ensure humanitarian access, in line with international humanitarian law."

In July humanitarian organisations distributed aid, including food and medications, to some 263,000 people out of at least 46 sites within the Raqqa region, Dujarric said.

The Syrian Democratic Forces, a Kurdish-Arab alliance backed by an international coalition battling IS, entered Raqqa city two months ago.

But the force's progress has been hindered by IS which is fighting hard to hang on to the de facto Syrian capital of the "caliphate" it self-proclaimed in June 2014.

The SDF is backed by the US-led coalition battling IS in Iraq and Syria, which has supplied weapons, air cover and a limited number of troops.

The fight for Raqqa has prompted tens of thousands of civilians to flee, with many wounded by crossfire or IS-planted explosive devices during their escape.

The Syrian conflict began when the Baath regime, in power since 1963 and led by President Bashar al-Assad, responded with military force to peaceful protests demanding democratic reforms during the Arab Spring wave of uprisings, triggering an armed rebellion fuelled by mass defections from the Syrian army.

According to independent monitors, hundreds of thousands of civilians have been killed in the war, mostly by the regime and its powerful allies, and millions have been displaced both inside and outside of Syria.

The brutal tactics pursued mainly by the regime, which have included the use of chemical weapons, sieges, mass executions and torture against civilians have led to war crimes investigations.