There has been renewed fighting in the Syrian city of Aleppo, as Amnesty International warned that new satellite images showed increased use of heavy weapons on residential areas.
The group said images revealed at least 600 probable artillery impact craters alone in the nearby town of Anadan.
Any attacks against civilians would be documented so that those responsible could be held accountable, it added.
Activists said shellfire had killed at least 12 people in Aleppo on Wednesday.
Among the dead were a woman and her two children in the al-Mashatiya district, the Syrian Observatory for Human Rights reported.
The UK-based group said at least 225 people were killed across the country on Tuesday, including 129 civilians, 50 rebels and 46 soldiers.
In a statement published on Wednesday, Amnesty said the new satellite images of Aleppo and its surrounding area showed "an increased use of heavy weaponry, including near residential areas".
Images from Anadan revealed more than 600 probable artillery impact craters from heavy fighting between Syrian armed forces and armed opposition groups, it added.
Amnesty said an image from 31 July showed probable artillery impact craters next to what appeared to be a residential housing complex in Anadan.
"Turning Syria's most populous city into a battlefield will have devastating consequences for civilians. The atrocities in Syria are mounting already," warned Christoph Koettl, emergency response manager for Amnesty International USA.
"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," he added.
Neither the government in Damascus, nor the rebel Free Syrian Army have publicly commented on Amnesty's claims.
However, independent experts the BBC has talked to agree with the group's interpretation of the images, the BBC's Mike Wooldridge reports.
On the ground, the army is said to have stepped up its bombardment of opposition-held areas of Aleppo.
State media reported that troops had clashed with "terrorists" in several places, inflicting heavy losses.
Activists estimate more than 20,000 people have been killed since the uprising against President Bashar al-Assad began in March 2011.
Reports of casualties often cannot be independently verified.