RIYADH, Saudi Arabia - Saudi Arabia's elderly King Abdullah died on Friday and was replaced by his brother Salman as the ruler of the world's top oil exporter and the spiritual home of Islam.
The royal court said in a statement that Abdullah, believed to be around 90 years old, died at 1:00 am local time (2200 GMT) on Friday, expressing its "great sadness and mourning".
The late monarch's half brother Moqren was named crown prince, according to the statement.
Abdullah will be buried later Friday following afternoon prayers, and citizens would be invited to pledge allegiance to the new 79-year-old monarch and the crown prince at the royal palace, the statement said.
Abdullah was hospitalised in December suffering from pneumonia and had been breathing with the aid of a tube.
Under Abdullah, who took the throne in 2005, Saudi Arabia has been a key US ally in the Arab world, most recently joining the US-led coalition carrying out air strikes against the Islamic State group in Syria and Iraq.
US President Barack Obama paid tribute to Abdullah as a valued ally.
"As our countries worked together to confront many challenges, I always valued King Abdullah's perspective and appreciated our genuine and warm friendship," Obama said in a written statement.
"The closeness and strength of the partnership between our two countries is part of King Abdullah's legacy."
As the top producer in the Organisation of the Petroleum Exporting Countries, Saudi Arabia has been the driving force behind the cartel's refusal in recent months to slash output to support plummeting oil prices.
Oil surged following Abdullah's death, with US benchmark West Texas Intermediate (WTI) for March delivery soaring as much as 3.1 per cent in New York.
"The market is probably uncertain over what the new king would do about this oversupply issue," said Daniel Ang, an investment analyst with Phillip Futures in Singapore.
Salman to follow brother's footsteps
The kingdom is also home to Islam's holiest sites, Mecca and Medina, and its role as a spiritual leader for Sunni Muslims has seen it vying for regional influence with Shiite-dominated Iran.
Salman, the new king, is widely expected to follow closely in his brother's footsteps, in foreign and energy policy as well as in making moderate reforms to the deeply conservative kingdom.
Abdullah pushed through cautious changes while in power, challenging conservatives with moves such as including women in the Shura Council, an advisory body.
He promoted the kingdom's economic development and oversaw its accession to the World Trade Organisation, tapping into the country's massive oil wealth to build new economic cities, universities and high-speed railways.
But the kingdom is still strongly criticised for a dismal human rights record, including the imprisonment of dissidents. Saudi Arabia is also the only country in the world that does not allow women to drive.
Salman is a stalwart of the royal family credited with transforming the capital Riyadh during his half-century as governor.
Recent years have seen concerns over his health after operations on his back, but Salman took on an increasingly high-profile role as Abdullah's own health issues forced him from the limelight.
Abdullah named Moqren as deputy crown prince last March, in an unprecedented move aimed at smoothing succession hurdles.
Moqren was a trusted confidant of Abdullah with a reputation as a liberal. A former air force officer born in 1945, Moqren is the youngest son of King Abdul Aziz bin Saud, the founder of Saudi Arabia.
Since King Abdul Aziz's death in 1952 the throne has systematically passed from one of his sons to another.
The streets of Riyadh were quiet following Abdullah's death but many Saudis turned to social media to mourn the king.
Abdullah Saadoon, a member of the Shura Council and retired general, said Abdullah had "laid the foundations of a blessed renaissance" in Saudi Arabia.
Another Twitter user, Shaima, said: "We didn't lose a king, we all lost a father".
Government-owned Saudi-1 television showed only a repeat of the official announcement.
Entertainment channels run by network MBC, which is privately owned by Sheikh Walid al-Ibrahim, a member of the royal family, switched to the company's Al-Arabiya news channel for continuous coverage of the king's death, mostly featuring file footage of Abdullah and Salman.