Hizbullah fired cluster munitions into northern Israel during this summer's 34-day war with the Jewish state, Human Rights Watch said in a report released on Thursday.
"This is the first time that Hizbullah's use of these controversial weapons has been confirmed," the group said in a press release.
"We are disturbed to discover that not only Israel but also Hizbullah used cluster munitions in their recent conflict," the release quoted Steve Goose, director of HRW's arms division, as saying.
"Use of cluster munitions is never justified in civilian-populated areas because they are inaccurate and unreliable," HRW added.
There was no immediate reaction from the Shia militia.
Israel has been roundly criticised for its use of cluster bombs during the war with Hizbullah that began on July 12 and ended with a UN-brokered cease-fire on August 14.
According to Israel's liberal Haaretz newspaper, the Jewish state's military dropped more than 1.2 million cluster bomblets into Lebanon during the month-long conflict.
HRW said that Hizbullah -- 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".