BEIRUT - Syria's regime has resorted to firing rockets containing cluster bombs, marking an expansion in its use of the banned munitions despite international condemnation, Human Rights Watch said on Monday.

The New York-based HRW has previously reported Syrian forces using air-dropped cluster bombs but in its latest statement said this had been expanded to the use of ground-based methods to spread the weapons.

"Syria is escalating and expanding its use of cluster munitions despite international condemnation of its embrace of this banned weapon," the director of HRW's arms division Steve Goose said in a statement.

"It is now resorting to a notoriously indiscriminate type of cluster munition that gravely threatens civilian populations."

The watchdog said that based on interviews with witnesses, analysis of around a dozen videos posted online by activists and photographs taken by an international journalist, it has concluded that regime forces have been using the Egypt-made munitions since early December.

It said evidence indicates that Syrian forces used BM-21 Grad multi-barrel rocket launchers to deliver cluster munitions in attacks near the city of Idlib in December 2012 and in Latamneh, a town northwest of Hama, on January 3, 2013.

"These are the first known instances of Syrian use of ground-based cluster munitions. No information is available on how or when Syria acquired these cluster munitions, which were made in Egypt," the statement said.

It cited a resident of Latamneh describing the January 3 attack.

"We heard a very loud sound and then a big explosion. After that we heard a series of smaller explosions," the resident said, adding that when he visited the sites of the attack he saw "bomblets spread out around 200 metres (yards)", including 20 which had not exploded.

He said that at the time of the explosions there were no warplanes flying overhead due to heavy fog.

According to him two residents were killed and 15 civilians, including women and young children, were wounded when the bombs exploded near an apartment building.

HRW said the Syrian army has Soviet-made BM-21 multi-barrel rocket launchers mounted on trucks and capable of firing 40 rockets almost simultaneously having a range of four to 40 kilometres.

Syria is not a party to the Convention on Cluster Munitions which bans the production, stockpiling, transfer and use of these weapons and also provides for the destruction of existing stockpiles.

More than 60,000 people have been killed in Syria since the start of an uprising against President Bashar al-Assad in March 2011, according to United Nations figures.