Israeli warplanes carried out intense airstrikes in eastern Syria early on Wednesday, apparently targeting positions and arms depots of Iran-backed forces as the region is on high alert. At least 57 fighters were killed and dozens were wounded, according to a Syrian opposition war monitoring group. A senior US intelligence official with knowledge of the attack told The Associated Press that the airstrikes were carried out with intelligence provided by the United States — a rare incidence of publicised co-operation between the two countries over choosing targets in Syria. The official said the strikes targeted a series of warehouses in Syria that were being used in a pipeline to store and stage Iranian weapons. The US official, who requested anonymity to speak about the matter, said US Secretary of State Mike Pompeo discussed Tuesday’s airstrike with Yossi Cohen, chief of Israel’s spy agency Mossad, at a public meeting in the popular Washington restaurant Café Milano on Monday. The Israeli air force carried out more than 18 strikes against several targets in an area stretching from the eastern town of Deir Ezzor to the Albu Kamal desert at the Syria-Iraq border, according to the Britain-based war monitor. For the past two years, Israeli air strikes have hit an area that extends from the southern countryside of Damascus to the Israeli-occupied Golan Heights, where a growing Iranian presence is regarded as a strategic threat by Israel. But air strikes also hit Albu Kamal, a remote area reportedly used to store missiles. . The most recent campaign of Israeli air strikes in Syria began in 2013, when Hezbollah stepped up the movement of equipment into the country, including long-range missiles to bolster its vast arsenal on the Lebanese border. Allied Iraqi militias on Tehran's payroll aided the effort – and have also been hit in Israeli raids. As Syrian President Bashar Al Assad's government floundered amid an increasingly powerful rebellion, Iran and its allies stepped up assistance to his regime. Tehran saw an opportunity to entrench itself in Syria and potentially open up a new rocket front along the Syria-Israel border. The purpose of this second front was to complement Hezbollah's positions in southern Lebanon, which bristle with an estimated 100,000 rockets. Ongoing Israeli air strikes, such as the attack in Albu Kamal overnight, are part of Israel's effort to stop the flow of arms to Hezbollah and Iran-allied forces near the Golan Heights.