Ahmed Hassan claims that forces loyal to the Libyan leader Colonel Gaddafi have used planes designed for crop spraying to deploy the weapons, defying the no-fly zone and destroying a series of fuel tanks.
Sky News is unable to verify the claim independently but has received photographs said to show the bombardment close to Misratah's port.
Under United Nations resolution 1973, no planes are allowed to fly in Libyan airspace except Nato planes tasked with enforcing the resolution to provide protection for civilians.
Misratah is Libya's third city and has been a centre of heavy fighting for more than two months.
Yesterday Amnesty International said that the siege in the city amounted to a possible war crime.
"The scale of the relentless attacks that we have seen by Gaddafi forces to intimidate the residents of Misrata for more than two months is truly horrifying," Amnesty senior adviser Donatella Rovera said.
"It shows a total disregard for the lives of ordinary people and is in clear breach of international humanitarian law," she said. Read More