The military chief of Syria's al-Nusra Front militant group has been killed in an air strike, the jihadist group has said on social media. Three other leaders were killed along with Abu Homam al-Shami, it says. Syria's state-run news agency said the army had targeted Nusra leaders as they met in northern Idlib province, the Associated Press reported. Al-Nusra is one of the most powerful groups fighting the army and has long been seen as an affiliate of al-Qaeda. It was involved in a major attack on the Air Force Intelligence headquarters in the embattled city of Aleppo on Wednesday.