Saudi Arabia's King Abdullah, the powerful U.S. ally who fought al-Qaida and sought to modernize the ultraconservative Muslim kingdom, including by nudging open greater opportunities for women, has died. He was 90.

A royal court statement said the king died at 1 a.m. on Friday. His successor was announced as 79-year-old half-brother, Prince Salman, a Royal Court statement carried on the Saudi Press Agency said.

Salman was Abdullah's crown prince and had recently taken on some of the ailing king's responsibilities. The 69 year-old Prince Muqrin, a former head of intelligence in Saudi Arabia and half-brother to both Salman and Abdullah, was announced as the kingdom's crown prince.

More than his guarded predecessors, Abdullah — who ascended to the throne in 2005 — assertively threw his oil-rich nation's weight behind trying to shape the Middle East. His priority was to counter the influence of rival, mainly Shiite Iran wherever it tried to make advances. He and fellow Sunni Arab monarchs also staunchly opposed the Middle East's wave of pro-democracy uprisings, seeing them as a threat to stability and their own rule.

Regionally, perhaps Abdullah's biggest priority was to confront Iran, the Shiite powerhouse across the Gulf. He backed Sunni Muslim factions against Tehran's allies in several countries, where colliding ambitions stoked proxy conflicts around the region that enflamed Sunni-Shiite hatreds — most horrifically in Syria's civil war, where the two countries backed opposing sides. Those conflicts in turn hiked Sunni militancy that returned to threaten Saudi Arabia.

Abdullah was selected as crown prince in 1982 on the day his half-brother Fahd ascended to the throne. He became de facto ruler in 1995 when a stroke incapacitated Fahd. Abdullah was believed to have long rankled at the closeness of the alliance with the United States, and as regent he pressed Washington to withdraw the troops it had deployed in the kingdom since the 1990 Iraqi invasion of Kuwait. The U.S. finally did so in 2003.

He was constantly frustrated by Washington's failure to broker a settlement to the Israel-Palestinian conflict. In 2000, Abdullah convinced the Arab League to approve an unprecedented offer that all Arab states would agree to peace with Israel if it withdrew from lands it captured in 1967. Alarmed by the prospect of a rift, President George W. Bush soon after advocated for the first time the creation of a Palestinian state alongside Israel.

Abdullah also pushed the Obama administration to take a tougher stand against Iran and to more strongly back the mainly Sunni rebels fighting to overthrow Syrian President Bashar Assad.

Expressing his condolences, President Barack Obama focused on Abdullah's efforts to nurture the kingdom's ties with the U.S.

"As a leader, he was always candid and had the courage of his convictions," Obama said. "One of those convictions was his steadfast and passionate belief in the importance of the U.S.-Saudi relationship as a force for stability and security in the Middle East and beyond."

Abdullah was born in Riyadh in 1924, one of the dozens of sons of Saudi Arabia's founder, King Abdul-Aziz Al Saud. Like all Abdul-Aziz's sons, Abdullah had only rudimentary education. His strict upbringing was exemplified by three days he spent in prison as a young man as punishment by his father for failing to give his seat to a visitor, a violation of Bedouin hospitality.

His aim at home was to modernize the kingdom to face the future. One of the world's largest oil exporters, Saudi Arabia is fabulously wealthy, but there are deep disparities in wealth and a burgeoning youth population in need of jobs, housing and education. More than half the current population of 20 million is under the age of 25. He was a strong supporter of education, building universities at home and increasing scholarships abroad for Saudi students.

Abdullah for the first time gave women seats on the Shura Council, an unelected body that advises the king and government. He promised women would be able to vote and run in 2015 elections for municipal councils, the only elections held in the country. He appointed the first female deputy minister in 2009. Two Saudi female athletes competed in the Olympics for the first time in 2012, and a small handful of women were granted licenses to work as lawyers during his rule.

One of his most ambitious projects was a Western-style university that bears his name, the King Abdullah University of Science and Technology, which opened in 2009. Men and women share classrooms and study together inside the campus, a major departure in a country where even small talk between the sexes in public can bring a warning from the morality police.

But he treaded carefully in the face of the ultraconservative Wahhabi clerics who hold near total sway over society and, in return, give the Al Saud family's rule religious legitimacy.

"He has presided over a country that has inched forward, either on its own or with his leadership," said Karen Elliot House, author of "On Saudi Arabia: Its People, Past, Religion, Fault Lines."

After the Sept. 11, 2001 terror attacks took place in the United States, Abdullah had to steer his country's alliance with Washington through the resulting criticism. The kingdom was home to 15 of the 19 hijackers, and many pointed out that the baseline ideology for al-Qaida and other groups stemmed from Saudi Arabia's Wahhabi interpretation of Islam.

When al-Qaida militants in 2003 began a wave of violence in the kingdom aimed at toppling the monarchy, Abdullah cracked down hard. For the next three years, security forces battled militants, finally forcing them to flee to neighboring Yemen. There, they created a new al-Qaida branch, and Saudi Arabia has played a behind-the-scenes role in fighting it.

The tougher line helped affirm Abdullah's commitment to fighting al-Qaida.

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Batrawy reported from Dubai, United Arab Emirates.