Fresh fighting has broken out between President Bashar al-Assad\'s forces and rebels rocking the capital Damascus and Syria\'s largest city, Aleppo.

Syrian forces pounded rebel positions in Aleppo, and explosions and gunfire have been reported across the region, including the outskirts.

Reports suggest a military jet roared across Aleppo followed by a huge explosion. Putting up a stiff fight, the rebels held on to the important district of Salaheddine in Aleppo. They also reportedly seized police stations to loot arms and ammunition.

Assad\'s forces, supported by helicopter gunships and tanks, stormed into Aleppo on 3 August in a bid to capture Salaheddine, a vital route for troops coming from the south.

Unverified online videos testify to the brutality of the Syrian regime.

\"The dead are more noticeable now; bodies are lying on the streets, and a stench comes from those who have been buried under the debris. There is echoing gunfire all around. No one is quite sure who is shooting at whom and there is an intimate proximity of the two sides,\" wrote Kim Sengupta of the Independent newspaper who was an eye witness.

Dozens of rebel fighters and civilians are believed killed by security forces in the last few days, although the exact number is not known.

The Syrian Observatory for Human Rights said at least 110 people had been killed across Syria on 3 August, of whom 88 were civilians.

Meanwhile, reports suggest Iranian troops have joined the regime\'s forces in fighting against the rebels. One activist leader claimed that more than 3,000 Iranian snipers had been drafted by the Syrian regime.

Forces loyal to Assad are now reportedly conducting house-to-house searches for rebels in the region.

\"The focus two weeks ago was on Damascus. The focus is now on Aleppo, where there has been a considerable build-up of military means, and where we have reason to believe that the main battle is about to start,\" the UN Under-Secretary-General for peacekeeping operations, Herve Ladsous, said.