The world's most devastating mines are the PFM-1 anti-personnel mines. This is a small, highly effective explosive and distributable mine used in warfare. Because of their shape and color, they are called "green parrot mines" or "butterfly mines." They are typically dropped in groups from aircraft at high altitudes over large areas. A pressure of 5 kilograms is enough to detonate this mine. However, these mines are so sensitive that they contain a delay mechanism (fuze) that is activated only upon impact with the ground. Once activated, the mine becomes indestructible; it requires the application of pressure over a long distance to destroy it. The use of these mines was banned in 1997 under the Ottawa Agreement. This is due not only to their impact on military units and civilians, but also because the most devastating feature of these mines is that children often mistake them for toys due to their shape and color.