The head of the world's chemical weapons watchdog on Monday defended a report into an alleged chlorine attack in Syria, despite a whistleblower's allegations of a cover-up. Fernando Arias said he stood by the investigation by the Organisation for the Prohibition of Chemical Weapons (OPCW) into the attack in the town of Douma in April 2018, in which around 40 people died. WikiLeaks released an email from a member of the team that probed the incident, which accused the OPCW of altering the original findings of investigators to make evidence of a chemical attack seem more conclusive. Britain, France and the United States unleashed missile attacks on suspected chemical weapons facilities run by Syrian President Bashar Al Assad's regime after the attack. "It is in the nature of any thorough inquiry for individuals in a team to express subjective views," Mr Arias said in his opening speech to the annual meeting of the OPCW's 193 member countries. "While some of these diverse views continue to circulate in some public discussion forums, I would like to reiterate that I stand by the independent, professional conclusion." Moscow and its allies have seized on the whistleblower's claims to back their insistence that the Douma attack was staged as a pretext for Western military action. Russia on Monday said the Douma report released in March 2019 "distorts reality" and reflects a "schism" in the organisation. France's ambassador to the OPCW, Luis Vassy, however expressed "full support and our total confidence in the conclusions of this report". Britain and the US also backed the watchdog. The Wikileaks email written by an investigator going by the alias "Alex" expresses the "gravest concern," saying the OPCW report was biased and "highly misleading and not supported by the facts". The email says the OPCW report changed the language on the levels of chlorine allegedly found to make it appear that the presence of the chemical was more conclusive. It also focuses on whether or not the chemical came from barrels found at the scene and how those barrels got there. If the barrels were dropped from the air it would indicate Assad's forces were responsible, whereas if they were put there manually it could indicate that the attack was staged by rebel forces. The row has fuelled tensions between Russia and the West over a new OPCW investigative team that is due shortly to name suspects behind chemical attacks - possibly including Douma - for the first time. OPCW states voted in 2018 to give the organisation new powers to pin blame on culprits for the use of toxic arms. Previously it could only confirm whether or not a chemical assault had occurred. The change was prompted by a series of chemical attacks in Syria - carried out despite Damascus agreeing to hand over its chemical arsenal in 2013 following a suspected sarin gas attack that killed 1,400 in the Damascus suburb of Ghouta. Moscow and its allies are now threatening to block next year's OPCW budget if it includes funding for the team. Mr Arias urged member countries "to ensure that the organisation has a budget in order for it to operate next year". The OPCW won the Nobel Peace Prize in 2013 and says it has eliminated 97 per cent of the world's chemical weapons.