The Britain-based Observatory for Human Rights said most of the victims were killed by airstrikes and barrel bombs dumped on eight rebel-held districts of the northern city yesterday.
The rest died from artillery shelling, sniper fire and in clashes between forces loyal to President Bashar Assad and rebels fighting to overthrow him.
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The bombings in Aleppo, Syria's largest city, are part of a campaign by Assad's forces to wrest control of neighbourhoods that were seized by rebels in mid-2012.
The Observatory has been documenting Syria's conflict since its start in March 2011 through a network of activists on the ground.
It released its report on the latest Aleppo casualties today, ahead of a trilateral meeting between senior US and Russian officials and UN mediator Lakhdar Brahimi, and Syrian government and opposition representatives in Geneva.
A second round of talks started in Switzerland on Monday but the discussions quickly became mired in acrimony as government and opposition delegates hurled accusations for the bloodshed taking place back home, failing to even agree on the talks' agenda.
From the outset, the talks have been accompanied by a sharp rise in violence on the ground.
The Observatory said that at least 4,959 people have died in Syria in the three-week period since January 22, when the government and opposition delegates sat down for the first round of face-to-face meetings in Geneva.
The Observatory said in a report yesterday that the period has seen the highest death toll since the uprising against Assad started nearly three years ago.
More than 130,000 people have died in the conflict since then, activist say. Millions of Syrians have been driven from their homes, some seeking shelter in neighbouring countries and others in safe parts of their homeland.