Kuwait’s Emir Sheikh Nawaf al-Ahmad al-Sabah died on Saturday aged 86, according to the royal court, just over three years after assuming power in the US-allied Gulf oil producer.

The cause of his death was not immediately disclosed. The emir was admitted to hospital late last month due to what the state news agency described at the time as an emergency health problem.

Crown Prince Sheikh Meshal al-Ahmad al-Sabah, 83, who has been Kuwait’s de facto ruler since 2021, when the frail emir handed over most his duties, was named as Sheikh Nawaf’s successor.

Kuwait announced 40 days of mourning and a three-day closure of official departments. World leaders paid tribute to Sheikh Nawaf and offered their condolences to his successor, the Al Sabah family and the people of Kuwait.

US President Joe Biden described Sheikh Nawaf as a “valued partner and true friend of the United States”, and pledged to “continue to strengthen the longstanding ties” between the countries.

Sheikh Nawaf became emir in September 2020 following the death of his brother, Sheikh Sabah, who had ruled for more than a decade and shaped the state’s foreign policy for more than 50 years.

Sheikh Nawaf was seen by diplomats as a consensus builder even though his reign was marked by an intense standoff between the government and elected parliament, which had hindered key structural reforms in the oil rich Gulf state. In recent months, consensus returned between the government and the parliament.

Kuwait, holder of the world’s seventh-largest oil reserves, borders Saudi Arabia and Iraq, and lies across the Gulf from Iran. It was invaded and occupied by Iraq in 1990, sparking the first Gulf war several months later in 1991 when the United States and other nations defeated Iraq and liberated Kuwait.

Since he took over in 2020, Sheikh Nawaf maintained a foreign policy that balanced ties with those neighbours, whilst domestically eight governments were formed under his rule.

Under Kuwait’s constitution, the crown prince automatically becomes emir but assumes power only after taking an oath in parliament. The new emir has up to a year to name an heir.

Analysts and diplomats say that Sheikh Nawaf and his crown prince Sheikh Meshal both appeared to align Kuwait more closely with regional powerhouse Saudi Arabia.

The new emir’s choice of crown prince and premier - who would be tasked with managing the government’s often stormy relationship with parliament - will be watched closely as a younger generation of Kuwait’s ruling family jostles for position.

Such factional struggles within the Al Sabah family have often played out in parliament as contenders for succession build their own political capital and domestic base.

Before handing over most of his constitutional duties to his designated heir, Sheikh Nawaf tried to secure a detente on the domestic political scene, including by issuing an amnesty pardoning dissidents that had long been sought by opposition figures.

But the stalemate continued, leaving Sheikh Meshal to try to put an end to the political bickering this year by dissolving parliament and holding early elections in June.

Kuwait bans parliamentary parties but is still one of the region’s most politically liberal states, with a voluble political debate and the region’s most powerful elected legislative assembly that includes Sunnis, Shi’ites, liberals and Islamists.

On Saturday, European Commission President Ursula von der Leyen and foreign policy chief Josep Borrell, said in a joint statement, Sheikh Nawaf would be remembered for his “unwavering dedication and commitment to serving his country, even in turbulent times.”

Emirati President Sheikh Mohamed bin Zayed wrote on X that Sheikh Nawaf had been a wise leader who played a major role in strengthening Kuwait-UAE relations.

British Prime Minister Rishi Sunak said he was saddened to hear of the passing of Sheikh Nawaf, who he described as a great friend of the United Kingdom who would be remembered fondly.