Iran's southwestern Khuzestan province, where a deadly attack left 24 dead in the city of Ahvaz on Saturday, is a key oil-producing region that has often complained of official neglect.
Bordering Iraq and the Gulf, it is one of the few areas in mainly Shiite Persian Iran to have a large ethnic Sunni Arab community.
The strategic frontier zone became part of modern Iran at the start of the 20th century after being squabbled over for hundreds of years by Persia and its rival, the Ottoman Empire.
Khuzestan was one of the major battlefields in the 1980-88 war between Iran and Iraq, with border city Khorramshahr becoming a symbol of national resistance after being ravaged by the bitter conflict.
During the war, Iraqi dictator Saddam Hussein hoped to peel Khuzestan off from Iran and seize control of its vast oil resources, but the population remained loyal to Tehran.
Nowadays the province contains the majority of Iran's oil deposits and accounted for over two-thirds of the country's production in 2016, official statistics said.
The region has been the focus of a separatist movement that is currently split among several groups based outside Iran.
In 2005 Khuzestan was hit by bloody clashes with Arab opposition groups and several attacks.
Tehran accused Western powers the United States and Britain of backing the violence.
Despite the region's natural riches the population of Khuzestan complain regularly of being forgotten by the authorities and of not benefitting from their oil wealth while still suffering the resultant pollution.
At the beginning of July the town of Abadan in the province was hit by several days of violent protests over water pollution.
Traditionally a very fertile area, the plains of Khuzestan have been battered regularly by droughts, with sandstorms increasing in recent years.