Amnesty International has released new satellite images which it says show an increased use of heavy weapons in and around Aleppo amid reports rebels have abandoned a stronghold in the city.
"We have retreated, get out of here," a lone rebel fighter told journalists.
Reports of rebel fighters leaving positions in the frontline Aleppo district of Salaheddine come a day after they were said to be running low on bullets as government forces encircled the area at the southern entrance to the city.
A Syrian government security source reportedly told Lebanon's Al-Manar television that Syrian forces are now in control of the Salaheddine district.
However, Wassel Ayub, a Free Syrian Army commander, insisted "the army is present in less than 15% of Salaheddin".
A close-up shows the damage next to a residential housing complex The Syrian army and rebel forces have been fighting for control of Aleppo - Syria's largest city and commercial centre - for almost a month.
The Amnesty images reveal more than 600 craters, which were likely caused by artillery shells, the organisation said.
An image from July 31 shows probable artillery impact craters next to what appears to be a residential housing complex in Anadan, a town northwest of Aleppo.
Amnesty said the images raise urgent concerns about the welfare of civilians and has warned both sides fighting in the city that they may be held criminally accountable for their failure to protect civilians.
The group's US emergency response manager, Christoph Koetti, said: "Amnesty International is sending a clear message to both sides in the fighting: any attacks against civilians will be clearly documented so that those responsible can be held accountable.
"Turning Syria's most populous city into a battlefield will have devastating consequences for civilians. The atrocities in Syria are mounting already.
A truck on fire near what is believed to be a civilian manned road block "The Syrian military and the opposition fighters must both adhere to international humanitarian law, which strictly forbids the use of tactics and weapons that fail to distinguish between military and civilian targets."
Meanwhile, Iran reiterated its support for Syrian President Bashar al Assad by sending a senior envoy to the Syrian capital Damascus.
Saeed Jalili, head of Iran's Supreme National Security Council, said Tehran would not let its close partnership with the Syrian leadership to be shaken by the uprising.
He said Iran would not allow the "axis of resistance" - a reference to itself, Syria, Hizbollah and Palestinian Islamist group Hamas - to be broken.
Iran also expressed fears for 48 Iranians it says are religious pilgrims kidnapped by rebels from a bus in Damascus while visiting Shi'ite shrines.
Seeking to restore his authority after suffering the gravest setbacks so far in the 17-month-old civil war, including the defection of his prime minister Riyad Hijab on Monday, Mr Assad made his first appearance on state television in two weeks on Tuesday and vowed to crush the uprising against his regime.
