DOZENS of people have been killed in a suspected chemical attack in a town in Syria’s northern Idlib province, opposition activists claimed.

The Britain-based Syrian Observatory for Human Rights monitoring group put the death toll at 58, saying there were 11 children among the dead. Meanwhile, the Idlib Media Centre said dozens of people had been killed.

Hours after the attack, a small field hospital in the region was struck and destroyed, according to a civil defence worker in the area. It was the third claim of a chemical attack in just over a week in Syria. The previous two were reported in Hama province.

The Syrian American Medical Society, which supports hospitals in opposition-held territory, said it had sent a team of inspectors to Khan Sheikhoun and an investigation was under way.

The Syrian activists had no information on what agent could have been used in the assault. They claimed the attack was caused by an air strike carried out either by the Syrian government or Russian warplanes. Russia’s defence ministry categorically rejected the claim that its planes attacked the town with chemical weapons.

The ministry said that “Russian air force planes haven’t dealt any strikes on Khan Sheikhoun in the province of Idlib”.

A Turkey-based Syrian woman whose niece, husband and one-year-old daughter were among those killed said the warplanes struck early, as residents were still in their beds. Makeshift hospitals soon crowded with people suffocating.

The province of Idlib is almost entirely controlled by the Syrian opposition. It is home to some 900,000 displaced Syrians, according to the United Nations. Rebels and opposition officials have expressed concerns that the government is planning to mount a concentrated attack on the crowded province. The reports came on the eve of a major international meeting in Brussels on the future of Syria and the region hosted by the EU’s High Representative, Federica Mogherini.

Claims of chemical weapons attacks, particularly the use of the chlorine agent, are not uncommon in Syria’s conflict. The worst attack was what a UN report said was an attack by toxic sarin gas in August 2013 on the Damascus suburb of Ghouta that killed hundreds of civilians.

The Syrian government has consistently denied using chemical weapons and chlorine gas, accusing the rebels of deploying it in the war instead.

Also, a joint investigation by the United Nations and the international chemical weapons watchdog determined the Syrian government was behind at least three attacks in 2014 and 2015 involving chlorine gas and the Islamic State group was responsible for at least one involving mustard gas.

The European Union’s top diplomat said Assad’s government must assume its responsibilities following reports of the attack in northern Syria. EU foreign policy chief Federica Mogherini said that “the news is awful” and that Assad’s government “has the primary responsibility of protecting its people and not attacking its people”.

She said the attack “is a dramatic reminder of the fact that the first priority is, as in any conflict, stopping the fighting”.

Meanwhile, Britain is urging Russia and China not to block action against those responsible for the suspected chemical attack, which it is calling “a war crime”.