Sarin is 20 times as deadly as cyanide. Within seconds of exposure noses run, tears form, mouths drool and vomit. If exposed to a high concentration, victim will convulse, become paralysed and die within 10 minutes. WHO experts took part in autopsies on victims of the chemical attack in a hospital in Adana, Turkey, in April. Credit:AP Turkish Justice Minister Bekir Bozdag said that the World Health Organisation supervised the autopsies and that the results were sent to The Hague for further analysis. Syrian Foreign Minister Walid al-Muallem rejected the findings from Turkey, denying the government had used chemical weapons in the past and maintained that it never would. At least 86 people were killed in the attack on the Syrian north-western town of Khan Sheikhoun, according to a tally from the health department in rebel-held Idlib Province, the New York Times reports. But the toll may not include victims evacuated to Turkey for treatment who have since died.

Meanwhile, demonstrations have erupted in London, New York, Los Angeles and parts of the United States against US President Donald Trump's order to fire 59 missiles at a Syrian airbase early on Friday morning following the chemical attack. Destroyed aircraft shelters in Syria, following strike orders from Donald Trump. Credit:DigitalGlobe/AP The Syrian army claimed nine civilians, including four children, were killed in Friday's aerial assault which, according to the Pentagon, were aimed at planes, depots and air-defence systems at the Shayrat Airfield. The field, between Damascus and Homs, was hit with Tomahawk missiles fired from the USS Porter and USS Ross, two destroyers in the Mediterranean. A crowd chants during a rally in opposition to the US air strikes in Allentown, Pennsylvania, one of the US's largest Syrian communities. Credit:AP

A statement from the Syrian army command described the attack as an act of "blatant aggression", saying it had made the United States "a partner" of Islamic State, the ex-Nusra Front and other "terrorist organisations". The office of Syrian President Bashar al-Assad, meanwhile, has called the US missile strike against the air base in central Homs "reckless" and "irresponsible", Associated Press reported. Protesters against the US strike at a Stop the War Coalition demonstration opposite Downing Street, London, on Friday. Credit:Getty Images Only hours after the attack, two war planes took off from the central Syrian airbase and carried out bombing raids nearby, according to the Syrian Observatory for Human Rights, targeting territory controlled by IS. A Syrian military source told Agence France-Presse that Syria's armed forces were warned about possible US military action hours before the strike and a number of airplanes were moved to other areas. US officials said Russia's military in Syria were informed beforehand in order to avoid casualties, AFP said.

Burnt and damaged hangars after they were attacked by US Tomahawk missiles on Friday. Credit:State Media/AP This is the first time the US has directly targeted Assad's forces. The Obama administration threatened to attack after previous chemical attacks, but did not. From his his Mar-a-Lago estate in Florida, Trump said his decision had been prompted in part by what he called failures by the world community to respond effectively to the Syrian civil war. A Syrian doctor treats a child following the chemical attack in Khan Sheikhoun, Syria. Credit:EMC/AP "Years of previous attempts at changing Assad's behaviour have all failed, and failed very dramatically. As a result, the refugee crisis continues to deepen, and the region continues to destabilise, threatening the United States and its allies."

But United Nations Secretary-General Antonio Guterres appealed to parties involved in the Syrian conflict for calm to avoid adding to the suffering. President Donald Trump speaks at Mar-a-Lago in Palm Beach after the US fired a barrage of cruise missiles into Syria. Credit:AP "Mindful of the risk of escalation, I appeal for restraint to avoid any acts that could deepen the suffering of the Syrian people," he said. The situation in Syria now "amounts to an international armed conflict" following the US missile strikes, according to the International Committee of the Red Cross. The guided-missile destroyer USS Ross fires a Tomahawk land attack missile towards Syria on April 7. Credit:AP

"Any military operation by a state on the territory of another without the consent of the other amounts to an international armed conflict," ICRC spokeswoman Iolanda Jaquemet said in Geneva. "So according to available information – the US attack on Syrian military infrastructure – the situation amounts to an international armed conflict." Russian President Vladi­mir Putin called for an immediate meeting of the UN Security Council and his spokesman, Dmitry Peskov, called the US missile strikes "violations of the norms of international law, and under a far-fetched pretext". US allies around the world expressed support, if sometimes cautiously, of Washington's strikes on Syria. Prime Minister Malcolm Turnbull said the strikes sent "a vitally important message" that the world would not tolerate the use of chemical weapons. "The retribution has been proportionate and it has been swift," he said. "We support the United States in that swift action."

Britain, France and Japan all expressed support. "The UK government fully supports the US action, which we believe was an appropriate response to the barbaric chemical weapons attack launched by the Syrian regime and is intended to deter further attacks," a British government spokesman said. Canadian Prime Minister Justin Trudeau urged an investigation into who was responsible for the chemical attacks before the US strike, according to Canada's Globe and Mail. Loading "There are continuing questions...that's why I'm impressing on the United Nations Security Council to pass a strong resolution that allows the international community to determine first of all who was responsible for these attacks and how we will move forward," he said.

Washington Post, Reuters, AP, with Tammy Mills