Islamic State claims attack at Atmeh killed fighters from two US-backed groups as they were crossing over from Turkish territory
The Islamic State (IS) group on Monday claimed a suicide bombing attack on a bus near a border crossing in Syria killed 50 US-backed rebels.
IS said the blast on Sunday at Atmeh killed fighters from the Failaq al-Sham and the Nour al-Din al-Zinki Movement groups, US-backed groups who were travelling to fight Islamic State in northern Aleppo province.
According to Medyan Dairieh, a journalist reporting on the Syrian conflict, the bombing killed dozens of fighters from the Free Syrian Army, and some Turkish policeman.
Turkey sent ambulances to help the injured, with reports of eight rebels being taken to hospitals in Turkey's Hatay province in critical condition.
The rest were being treated in Syrian hospitals, Turkish media reported.
— The 'Nimr' Tiger (@Souria4Syrians) 14 August 2016
Pictures circulating on social media showed the burnt-out remains of a bus and medics treating wounded people.
The Syrian National Coalition, a Turkey-based political alliance opposed to the Syrian government, condemned the attack as further proof that IS is working with the Syrian government.
"The bombing targeted innocent people and charities who are helping the needy in Aleppo," it said. "This is proof that ISIS is working with the Syrian government.
"This will not stop us but unite us further against the Syrian regime, Iran and all its allies."
Turkey's CNN Turk television reported that the explosion occurred at the entrance to the Atmeh refugee camp in Syria, near the frontier crossing, citing local sources.
The Syrian Observatory for Human Rights, a UK-based activist group, said it had received reports that two Turkish soldiers had been killed in the attack.
Syria's Idlib province, where Atmeh is located, is a bastion of the Turkey-backed opposition to President Bashar al-Assad's rule.
The Atmeh border crossing has also been a vital route used for delivering aid and supplies to rebel-held areas in the north of Syria.