Ammonium nitrate as an explosive
Pure ammonium nitrate is not an explosive on its own. It is classified as an oxidiser (Grade 5.1) under the United Nations classification of dangerous goods. If mixed with ingredients like fuel or some other contaminants, or because of some other external factors, it can be very explosive.
However, for combinations to explode, triggers like detonators are required. Many Improvised Explosive Devices (IEDs) used by terrorists around the world have ANFO as the main explosive, triggered by primary explosives like RDX or TNT. In the majority of terror attacks in India, including those in Pulwama, Varanasi, Malegaon, Pune, Delhi, Hyderabad, and Mumbai, ammonium nitrate has been used along with initiator explosives like RDX.