Fierce fighting between Syrian forces and the rebels is continuing as opposition groups vowed to make Aleppo the grave of President Bashar al-Assad and his regime.

As the battle entered the fourth day on 31 July, rebel forces held on to key Aleppo neighbourhoods.

"We always knew the regime's grave would be Aleppo. Damascus is the capital, but here we have a fourth of the country's population and the entire force of its economy. Bashar's forces will be buried here," a rebel fighting in Aleppo told Reuters.

Hospitals and makeshift clinics in Syria's most populous city are flooded with badly injured people. Scores of dead bodies are said to be piling up in hospitals.

"Some days we get around 30, 40 people, not including the bodies. A few days ago we got 30 injured and maybe 20 corpses, but half of those bodies were ripped to pieces. We can't figure out who they are," a medic in Aleppo told Reuters.

Reports suggest that more than 40 people died on 30 July, out of which 30 were said to be civilians.

Both sides claim control of Salaheddine district, a place of strategic importance in Aleppo. The rebels refuted the government's claim of taking control of Salaheddine. The district has a vital route for troops coming from the south.

Despite the rebels' concerted efforts to capture the capital Damascus two weeks back, they were driven away by Assad's forces.

Helicopter gunships and tanks of the Syrian forces continue their attacks, while poorly armed rebels manage with their weapons.

Several unverified videos have been uploaded by activists showing the severity of the latest violence in Aleppo.

Tens of Thousands of residents have already fled Syria's commercial capital. The nearby bordering districts in Turkey have been flooded by Syrian refugees.

In another blow to the regime, the senior most diplomat in Assad's government has defected from the regime. Charge d'affaires Khaled al-Ayoubi in London has abandoned the regime following a series of defections.