"At least 44,063 people have been killed in 21 months," said Syrian Observatory for Human Rights director Rami Abdel Rahman.
He said they were 30,819 civilians, 1,482 defectors, 10,978 soldiers and 784 people whose identities were impossible to document.
The Observatory counts non-military combatants who have taken up arms against the regime as civilians.
"Thousands of the civilians were rebels," said Abdel Rahman.
The actual number of people killed in violence is probably much higher, he added.
"Many of the thousands missing in Syria's jails are feared dead," said Abdel Rahman.
"In addition, neither the rebels nor the army are disclosing the real number of people killed among their ranks, for fear of hurting morale."
The Observatory does not include in its toll "thousands of shabiha (pro-regime militia members), people believed to be informants for the state, or foreign fighters who have joined the insurgency."
It said 93 people were killed in violence nationwide on Wednesday.
More than 44,000 people have been killed in Syria since the outbreak in March 2011 of an anti-regime revolt that became a bloody insurgency after a brutal crackdown, a rights group said on Wednesday.