Human Rights Watch accused Syria on Tuesday of stepping up its use of internationally banned cluster bombs despite assertions by Damascus that it is not deploying the munitions at all.

A report by the New York-based watchdog said data "shows an important increase in the use of cluster bombs in the past two weeks" in Idlib, Homs, Aleppo, Deir Ezzor and Damascus provinces.

"Syria's denial is meaningless as evidence mounts that cluster bombs are raining down on towns and villages," said Steve Goose, HRW arms director.

The air force "is imposing a reign of terror on civilians in rebel-held areas across the country with cluster bombs and other explosive weapons," he added in a statement, claiming there had been an upturn in the past two weeks.

"The cluster bomb strikes are part of an intensifying air campaign by government forces on rebel-held areas that has included dropping high explosive, fragmentation and even improvised 'barrel' bombs into populated areas."

The report also said that a review of markings on the bombs and sub-munitions "show that they were manufactured in the 1970s and early 1980s at Soviet state munitions factories."

On October 14, Goose accused the regime of President Bashar al-Assad of dropping cluster bombs into populated areas.

The following day, the Syrian army denied using cluster munitions, saying it did not even have such weapons in its arsenal.

Syria has not ratified a convention banning cluster bombs that has been adopted by 109 countries since 2008.