The group said that Hezbollah had fired two Chinese-made rockets carrying cluster munitions at the Galilee village of Mghar on July 25, killing one person and injuring six others.
An Israeli police spokesman, Mickey Rosenfeld, told Aljazeera they had found evidence of 113 cluster bomb rockets being fired on Israel during the month-long conflict, far fewer than the number dropped by Israel on southern Lebanon.
Up to one million unexploded cluster bomblets may remain in southern Lebanon, a report by the Landmine Action group said on Wednesday.
The Israeli weapons have killed at least 21 people and wounded more than 100 others across southern Lebanon following the ceasefire, and Israel has itself been condemned by the UN and human rights groups for their use.
A Hezbollah spokesman told Aljazeera the organisation was investigating the claims made in the Human Rights Watch (HRW) report.
"There are many, many false reports from Israeli sources. And they are all lies," Hussein Rahal said.
Steve Goose, director of HRW's arms division, said it was the first time Hezbollah's use of the controversial weapons had been confirmed.
"We are disturbed to discover that not only Israel but also Hezbollah used cluster munitions in their recent conflict," Goose said in a statement
Cluster bombs have been found
all over southern Lebanon
"Use of cluster munitions is never justified in civilian-populated areas because they are inaccurate and unreliable."
Cluster munitions spread bomblets over a wide area from a single container.
The bomblets often do not explode on impact, but can do so later at the slightest touch, making them similar to anti-personnel landmines.
The use of such bombs near civilian populations is forbidden by international humanitarian law.
Human Rights Watch said that Hezbollah - which launched nearly 4,000 rockets into Israel during the war - had used Chinese-made Type-81 122 millimetre rockets, "the first confirmed use of this particular model of cluster munitions anywhere in the world".
Each one carries 39 submunitions capable of shooting out hundreds of ball bearings, the group said.
Israeli police said that one person had been killed and 12 injured during the conflict by cluster bombs, although none had been injured since the end of the war.
Rosenfeld said the police and military were continuing an operation to locate all the rockets fired at Israel during the conflict.
"There is always the possibility that we could find more cluster bombs," he said.