One military source, who was not authorised to speak publicly, said the strikes had targeted a runway in the sprawling air base that is located southeast of Homs city.The runway and underground facilities at Shayrat, including aircraft shelters, have undergone a major expansion by the Russia military in the last three years, the military source said.Opposition military sources say Iranian militias hold sway in large swathes of western Homs province near the Lebanese border and to the east where they have a string of bases.Iran, which poured thousands of it's Shi'ite militias to help Syrian President Bashar al Assad win his battle against insurgents, says its military presence in Syria is limited to a limited number of advisors.Israel has been mounting attacks in Syria for years against what it has described as Iranian and Iran-backed forces that have deployed there during the war, which began more than a decade ago."