"In late 1991 or 1992, discussions in Sudan between al Qaeda and Iranian operatives led to an informal agreement to cooperate in providing support—even if only training—for actions carried out primarily against Israel and the United States. Not long afterward, senior al Qaeda operatives and trainers traveled to Iran to receive training in explosives. In the fall of 1993, another such delegation went to the Bekaa Valley in Lebanon for further training in explosives as well as in intelligence and security. Bin Ladin reportedly showed particular interest in learning how to use truck bombs such as the one that killed 241 U.S. Marines in Lebanon in 1983. The relationship between al Qaeda and Iran demonstrated that Sunni-Shia divisions did not necessarily pose an insurmountable barrier to cooperation in terrorist operations". . .In early November 1998, the U.S. government indicted various al Qaeda members for the embassy bombings. The indictment included this sentence: "Al Qaeda also forged alliances with the National Islamic Front in the Sudan and with the government of Iran and its associated terrorist group Hezbollah for the purpose of working together against their perceived common enemies in the West, particularly the United States.":
The Al Qaeda-Iran ConnectionThe June 1996 conference in Tehran, for example, which was attended by Ramadan Shallah (Palestinian Islamic Jihad), was also attended by Ahmad Salah (Egyptian Jihad), Imad Mugnyeh (Lebanese Hizbollah), Ahmad Jibril (PFLP-GC), Imad al-Alami and Mustafa al-Liddawi (Hamas), George Habash (PFLP), and a representative of terrorist financier Osama bin-Ladin. Tehran and Terrorism: Iran Under President Muhammad Khatami (1998)
Iran Admits To Facilitating 9/11 Terror Attacks: Top Iranian official admits for first time Iran aided al Qaeda terrorists (2018)