President Bashar al-Assad's forces have unleashed an airstrike on the rebels in Aleppo as new UN-Arab League special envoy Lakhdar Brahimi takes over.
The aerial attack is believed to have killed more than 25 people in al-Bab district in Syria's largest city near the Turkish border; several others, including women and children, were reportedly wounded.
Unverified videos have been posted online showing the severity of the air attack which left people frantically searching for bodies buried in the debris.
A vast swathe of the strategically important Aleppo province is under rebel control, which has become a major worry for the Assad regime.
The violence has escalated in recent weeks as an opposition group put the death toll at 23,000 in the 17-month uprising. More than 5,000 people have been killed in August 2012 alone, making it the bloodiest month.
At this critical juncture, the veteran Algerian diplomat Brahmi is likely to hold talks with Assad. In an indication of what could transpire, Assad's regime has made it clear that it would do everything possible to make Brahimi's job tougher.
Syrian Information Minister Omran Zoabi said Brahimi would not be successful unless the rebels' outside support is ended.
"The conditions for success for Lakhdar Brahimi in his mission is for specific countries - Qatar, Saudi Arabia and Turkey - to announce their commitment to the six-point plan and completely stop sending weapons (to rebels) and close borders to fighters and close fighter training camps," Zoabi said during a news conference in Damascus.
Hinting at the non-weapon support given by outside countries, Zoabi said: "The ball is not in the Syrian court, the ball is in the Saudi, Qatari, Turkish, European and US court."
The peace plan initiated by Brahimi's predecessor Kofi Annan failed because both Syrian forces and the rebels failed to adhere to it.
Peter Maurer, President of the International Committee of the Red Cross (ICRC) has also arrived in Syria to hold talks with Assad.
"At a time when more and more civilians are being exposed to extreme violence, it is of the utmost importance that we and the Syrian Arab Red Crescent succeed in significantly scaling up our humanitarian response. It is vital that we build on what has already been achieved on the ground," said Maurer kicking off his three-day visit to Syria.
Maurer will also meet senior figures in the Syrian polity to stress the importance of establishing a safe environment for civilians.