Pro-government forces in Libya have been accused by a human rights campaign group of using cluster bombs, which are banned by more than 100 countries.
Human Rights Watch said one of its photographers saw three mortar-launched projectiles explode over a residential area of Misrata.
A Libyan government spokesman denied the allegation.
Government troops have intensified their siege of Misrata, the only western Libyan city still in rebel hands.
The BBC's Orla Guerin reports from inside the battle-scarred city that local residents fear a massacre without greater action by Nato air forces to break the siege.
As well as cluster munitions there have been a number of reports that Libyan forces are using the Soviet-designed Grad rocket system in their bombardment of Misrata.
The Grad, which launches multiple rockets from mobile launchers, has been blamed for a number of civilian deaths in recent days, including eight people in a bread queue.