Human Rights Watch has accused forces loyal to Muammar Gaddafi of using cluster bombs in attacks against Misurata.
The group says it observed at least three such weapons explode over the city two days ago.
The Libyan government has denied the allegations.
Cluster bombs are banned by more than 100 countries.
They cannot be targeted, and pose a grave risk to civilians when fired near populated areas.
Fred Abrahams, a special adviser for Human Rights Watch, based in New York, spoke to Al Jazeera about what his group had found in Misurata.