"Syria is expanding its relentless use of cluster munitions, a banned weapon, and civilians are paying the price with their lives and limbs," said Steve Goose, director of the arms division at Human Rights Watch.
"The initial toll is only the beginning because cluster munitions often leave unexploded bomblets that kill and maim long afterward."
The Syrian government did not immediately respond to a CNN request for comment.
In October, Syrian armed forces denied the possession or use of cluster bombs.
A statement released through the state-run Syrian Arab News Agency said "misleading media outlets" had published "untrue news claiming the Syrian Arab Army has been using cluster bombs against terrorists."
The Syrian army "does not possess such bombs," it said, adding that the media reports were "aimed at diverting the public opinion from the practices of the armed terrorist groups against civilians."
The Human Rights Watch report is based on field investigations, analysis of video footage posted by activists and eyewitness reports, it said.
The collection of data does not include details of casualty numbers but many deaths and injuries have been documented, the group said.
"Remnants of at least 156 distinct cluster bombs have been identified so far from the video footage," the group said.
"Human Rights Watch has documented government use of cluster munitions, both air-dropped and ground-delivered, but it has seen no evidence of cluster munition use by opposition rebel groups."
Weapons are indiscriminate
Another rights group, Amnesty International, has accused the Syrian government of using cluster bombs in civilian areas.
"Civilians continue to be at the receiving end of increasingly frequent indiscriminate attacks by Syrian government forces," Amnesty said in a report Thursday.
"Internationally banned cluster munitions are being used daily against civilian residential areas in towns and villages, in utter disregard for the most fundamental principles of international humanitarian law."
The report said the "vast majority" of abuses were committed by Syrian government forces, but that rebel groups are also carrying out abuses such as kidnapping and summary executions.
Syria is not one of the 111 states worldwide that have signed up to the Convention on Cluster Munitions, which bans their use. The United States also is not a signatory.
Cluster munitions are widely viewed as unacceptable because the bomblets spread across a wide area and make no distinction between civilians and fighters.
CNN cannot independently verify death tolls or other accounts of violence in Syria.
Last month, U.N. High Commissioner for Human Rights Navi Pillay said about 70,000 people had been killed in the two-year-old conflict.