Kuwait's Emir Sheikh Sabah al Ahmed al Sabah has died at the age of 91, depriving the Persian Gulf of a ruler who often played a key part in trying to settle disputes in the volatile region.

Oil policy in Opec's major producer is unlikely to change, however. A smooth succession is assured, with his 83-year-old half-brother and crown prince, Sheikh Nawaf al Ahmed, expected to take over.

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Opec Secretary General Mohammad Barkindo said the late Kuwaiti Emir played a significant role in paving the way for the creation in 2016 of the Opec+ group that includes leading producers such as Russia. The alliance has altered production in line with market changes to ensure price stability

Kuwait, which is capable of pumping 3 million barrels per day of oil, is currently the fourth-largest crude exporter in the Middle East behind Saudi Arabia, Iraq and the United Arab Emirates.

'Dean or Arab diplomacy'

Sheikh Sabah was flown to the US for medical treatment in July following surgery for an unspecified condition in Kuwait.

He had ruled the oil-rich Gulf Arab state since 2006 and had overseen its foreign policy for more than 50 years.

He was dubbed the "dean of Arab diplomacy" for his efforts to restore relations with states that backed Iraq during its 1990-1991 invasion of Kuwait.

Sheikh Sabah also acted as a mediator in regional disputes, including the ongoing diplomatic stand-off between Saudi Arabia and Qatar. He distanced himself from taking sides in the US-Iran hostilities.

Kuwait also refrained from intervening in Syria's civil war, instead hosting several donor conferences for humanitarian aid.

Despite being ruled by ageing men from the long-standing Al Sabah dynasty, Kuwait stands out among the conservative Gulf Arab states thanks to a vociferous opposition and an elected parliament that often calls government ministers to account.

Kuwait’s parliament has long prevented the government from giving a role to international oil companies in investing in the emirate’s upstream sector.

This has stymied efforts to develop complex sour and tight gas projects, resulting in domestic gas shortages and forcing Kuwait to import liquefied natural gas to feed power generation.

''Sheikh Sabah dedicated his life to the State of Kuwait, as foreign minister, prime minister and since January 2006 as the Emir. He has provided a steady hand and wise counsel in guiding his country both at home and through the often choppy waters of international affairs," Barkindo said.

"He channelled great energies into developing the State of Kuwait, supporting and encouraging its people and has acted as a bridge builder and mediator in helping solve many regional and international disputes."