Human Rights Watch said on Monday that it had taken photographs of cluster grenades stored by Israeli artillery teams on the Israel-Lebanon border.
It also said that a cluster grenade attack on Wednesday killed one and wounded at least 12 civilians in the village of Blida.
"Cluster munitions are unacceptably inaccurate and unreliable weapons when used around civilians," Kenneth Roth, Human Rights Watch executive director, said in a statement.
"They should never be used in populated areas."
An Israeli army statement said: "The use of cluster munitions is legal under international law and the ... [Israeli military] uses such munitions in accordance with international standards. We are checking the specific details of the incident mentioned in the report."
Violating a ban?
Human Rights Watch said it had photographed M483A1 artillery shells stored on the Israeli side of the border, which deliver 88 cluster sub-munitions per shell and have a failure rate of 14 per cent, often leaving behind dangerous unexploded shells.
It said it believed the use of cluster grenades in populated areas could violate a ban on indiscriminate attacks contained in international humanitarian law.
"Our research in Iraq and Kosovo shows that cluster munitions cannot be used in populated areas without huge loss of civilian life," Roth said.
"Israel must stop using cluster bombs in Lebanon at once."