Islamic State militants have fired a rocket in northern Syria that caused symptoms of “chemical gas” exposure in 22 Syrian rebels, state media cited Turkey’s military as saying on Sunday. The attack targeted Turkey-backed rebels who have for days been besieging the Islamic State-controlled town of al-Bab, a major goal in Ankara’s “Euphrates Shield” operation to push the jihadists away from the Syrian side of the Turkish border. According to the state-run Anadolu agency, the Islamic State rocket attack occurred in the Haliliye area. The army did not specify where the attack had taken place. “Twenty-two rebels were observed to have symptoms of being exposed to chemical gas in their eyes and bodies as a result of the rocket fired by Daesh,” media reports quoted the army statement as saying, using an Arabic acronym for Islamic State. The rebels were transferred to a hospital in Turkey’s border province of Kilis on suspicion of chemical poisoning after complaining of constant sickness and severe headaches, Hurriyet newspaper reported on its website. Turkish AFAD emergency relief teams conducted various tests on them to check for traces of chemical, other media reported. In the last 24 hours around al-Bab, Turkish jets have destroyed four Islamic State targets in the Anifah region, and one Turkey-backed Syrian rebel has been killed and 14 wounded in clashes, the military said. On Thursday, three Turkish soldiers were killed in an air strike in Syria which the army said it believed was carried out by the Syrian air force. It happened on the first anniversary of Turkey’s downing of a Russian jet over Syria and raised fears of an escalation in the conflict. After the air strike, Dogan news agency said on Saturday Turkey deployed low-altitude air defense systems with Stinger missiles to Gaziantep province on its Syrian border. Turkey’s President Tayyip Erdogan discussed the air strike with Russian counterpart Vladimir Putin on Friday. They spoke again late on Saturday about “Syria and efforts to resolve the humanitarian drama in Aleppo”, sources in Erdogan’s office said. Russia is Syrian President Bashar al-Assad’s main military backer. Turkey backs rebels fighting to oust him. Ankara and Moscow only restored ties, which had been damaged by November’s jet incident, in August. While they continue to pursue conflicting goals in Syria, Turkey has of late been less openly critical of Assad than in the past.