ISIS may launch devastating chemical attacks in Europe: UN watchdog

London: Islamic State terrorists fleeing Iraq and Syria may launch devastating chemical attacks in Europe, an inquiry by the UN's global chemical weapons watchdog has warned.

The fleeing terrorists could carry out mustard gas attacks after learning how to use the toxic substance in battle zones, a senior official from Organisation for the Prohibition of Chemical Weapons (OPCW) global chemical weapons warned at a defence conference in Paris this week.

"It seems that one of the dangers that we need to face and have a response for since ISIS has learnt how to make mustard gas is that sadly one of the people who learnt how to do it comes back to one of our countries and helps carry out an attack like this," said Philippe Denier, director at the verification division of the OPCW.

Mustard gas is a powerful irritant that targets the skin, eyes and airways, and can kill in large enough or highly concentrated enough amounts. Symptoms can take up to 24 hours to appear.

The inquiry, conducted last month, found that ISIS had used the weapon on civilians.

After rockets containing traces of mustard gas were used on US troops in northern Iraq in September, Marine General Joseph Dunford, chair of the Joint Chiefs of Staff, told the US Senate's Armed Services Committee that while ISIS' capabilities are currently "rudimentary" the attack was a "concerning development", the Independent reported.

Last month, the European Union's Security Commissioner, Julian King, had warned that the huge military operation to remove ISIS from its last Iraqi stronghold could spark an exodus of fighters back to European countries, increasing the risk of terror attacks.