text: On 31 July 1987, during the Hajj pilgrimage in Mecca, a clash between Shia pilgrim demonstrators and the Saudi Arabian security forces resulted in the death of more than 400 people. The event has been variously described as a "riot" or a "massacre". It developed from increasing tensions between Shia Iran and Sunni Saudi Arabia since the 1979 Iranian Revolution. Since 1981, Iranian pilgrims have held a political demonstration against Israel and the United States every year at Hajj, but in 1987, a cordon of Saudi police and the Saudi Arabian National Guard sealed part of the planned demonstration route, resulting in a confrontation between them and the pilgrims. This escalated into a violent clash, followed by a deadly stampede.