Human Rights Watch Thursday said that hundreds of victims of a chemical weapons attack in Syria remained without justice one year on, days after Damascus's stockpile was completely destroyed.

The report came as a monitor said Syria's three-year war has now killed more than 180,000 people, and as France announced it delivered weapons to rebels battling to topple the regime months ago.

Thursday was the first anniversary of the chemical attack on the capital's Ghouta region, a stronghold of the rebel movement, which the United States estimated killed up to 1,400 people.

Images of the lifeless bodies of children -- some 426 died -- shocked the world and the finger of blame was quickly pointed at Syrian troops loyal to President Basher al-Assad, who denied involvement.

After a global outcry and American threats to strike regime positions, Assad agreed to an international plan to destroy Syria's chemical weapons stockpile.

On Monday, US President Barack Obama hailed the completion of the destruction, which was carried out aboard a US Navy ship in the Mediterranean.

"Important though it is, the removal of chemical weapons from Syria's arsenal will do nothing for the hundreds of victims who died a year ago and the relatives who survive them," said Nadim Houry, Deputy Middle East and North Africa Director at HRW.

"Closure of the chemical weapons issue in Syria will be possible only when those who ordered and executed the Ghouta attacks have been held to account and are behind bars," he added.

The HRW statement also said that "available evidence strongly suggests that Syrian forces carried out the attack".

"International efforts to ensure credible justice for these and other ongoing grave human rights crimes in Syria have proved elusive," the New York-based body added.

In a statement, the opposition Syrian National Council said that the perpetrators had gone "unpunished" and that "crimes against humanity" were still being committed with other weapons.

French President Francois Hollande, meanwhile, said that his government delivered weapons to the Syrian rebels battling to overthrow the Damascus regime "a few months ago".

He said the deliveries were made when so-called moderate rebels were fighting both Assad's forces and Islamic State jihadists, Hollande said.

The conflict in Syria erupted in March 2011, with peaceful anti-government protests that the authorities responded to with force.

In three years, more than 180,000 people have been killed, including 58,805 civilians, said the Britain-based Syrian Observatory for Human Rights which relies on a network of sources on the ground.

The new toll includes 49,699 members of the armed opposition as well as 66,365 regime forces, it said.

One of the regime's latest casualties was an anti-aircraft defence unit officer killed along with three bodyguards by a mine as they carried out an inspection near Mleiha, a former rebel stronghold southeast of Damascus that the army recaptured this month.