This article has been updated on Saturday November 12.
Russia has called for international inspectors to send an urgent mission to Aleppo after saying it has evidence that opposition rebels had used chemical weapons against troops and civilians.
The claims have been denied by an opposition group.
Meanwhile an international watchdog has voted to condemn the use of chemical weapons by the Syrian government and the self-styled Islamic State.
The Defence Ministry in Moscow said Russian personnel had found unexploded artillery shells with toxic chemicals, launched by terrorists, in southwestern Aleppo.
According to the Russian agency Interfax, the zone was recently seized by rebels from government forces. Samples are also said to have been taken from areas where shells landed, including fragments of shells that exploded.
The shells have been tested in a mobile laboratory.
“Express analysis of the samples has shown that the weapons contained chlorine and white phosphorus,” said one unnamed Russian expert.
Reports say the samples are to be further analysed in Russia at a scientific facility licensed by the Organisation for the Prohibition of Chemical Weapons (OPCW).
The Russian Defence Ministry claims militants repeatedly used chemical weapons in their attempts to break through Syrian army lines.
The opposition Syrian National Coalition, based in Istanbul, issued a statement denying the Russian allegations, saying that chemical weapons had only been used by the Assad regime and its allies.
The executive body of the global chemical weapons watchdog voted on Friday to condemn the use of banned toxic agents by the Syrian government and ISIL militants. It also authorises international inspections at sites in Syria.
Reuters quoted a source as saying that roughly two-thirds of the 41 members on the Executive Council of the Organisation for the Prohibition of Chemical Weapons (OPCW) endorsed the text.
The vote is described as unusual as the executive council of the body based in The Hague generally operates through consensus. But the text was reportedly supported by 28 members, including Germany, France, the United States and Britain. It was opposed by Russia, China, Sudan and Iran.
The British Foreign Office released a statement in which Foreign Secretary Boris Johnson condemned the use of chemical weapons in Syria, singling out “the Assad regime and Daesh” (ISIL).
Some reports say the vote represents a watered-down compromise on original plans by the Obama administration to impose penalties on Damascus and force President al-Assad’s government to destroy chemical stockpiles – but still mark an important advance in attempts to hold offenders to account.
An international inquiry lasting over a year by the OPCW and United Nations concluded that Syrian government forces were responsible for the use of chlorine barrel bombs against civilians.
The Syrian army backed by Russian forces have been trying to oust rebels in an attempt to take control of Aleppo in what would be a major strategic victory in the five-year conflict. Their bombings of civilian areas have been condemned by western powers as war crimes. Moscow blames failure by the US to rein in extremists within the rebels’ ranks for the ongoing fighting.
In a separate development, the Syrian government’s military media released a video on Friday, which it said shows rebels firing upon each other before realising that they were on the same side.
According to AP, the video could not be independently verified.
According to the Syrian authorities it came from the helmet camera of a militant fighting with Fatah al-Sham – a group linked to al-Qaeda formerly known as the Nusra Front.
The fighter wearing the camera then falls to the ground after apparently being wounded – he is said to have died.