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Carolyn Kaster, File, Associated Press
FILE - In this March 25, 2015 file photo, then Saudi Arabian Ambassador to the U.S. Adel Al-Jubeir speaks during a news conference at the Royal Embassy of Saudi Arabia in Washington. On Wednesday, April 29, 2015, King Salman replaced Foreign Minister Saud al-Faisal with Adel al-Jubeir, the ambassador to the U.S., who is not a member of the royal family but has been the public face of the Yemen air campaign.

RIYADH, Saudi Arabia — Saudi Arabia's King Salman redrew the line of succession on Wednesday, appointing a counterterrorism czar as crown prince and placing his own defense minister son in line for the crown — a dramatic reshuffle that reflects the kingdom's mounting security concerns and more assertive foreign policy.

The move comes just three months after Salman ascended to the throne, at a time when Saudi Arabia is struggling to contain its regional rival, Iran, while fending off a growing threat from the Islamic State group.

The appointments, announced in several royal decrees, thrust a new, younger generation of princes into the line of succession and map out the future of the throne for potentially decades to come.

The 79-year-old king appointed his nephew, Prince Mohammed bin Nayef, as crown prince. The 55-year-old prince, who also serves as interior minister and was previously deputy crown prince, has led the kingdom's crackdown on Islamic militants and has worked closely with Western security and intelligence agencies. He has survived several assassination attempts, including one in 2009 by al-Qaida.

The prince becomes the first from among his generation to be elevated to such a high position. He replaces Prince Muqrin, Salman's half brother, who had widely been seen as a transitional figure.

The king's son, Prince Mohammed bin Salman, was named deputy crown prince, placing him as the most likely second in line for the crown. He is believed to be around 30 years old, and as defense minister has assumed a leading role in the Saudi-led air campaign against Iranian-backed Shiite rebels in Yemen.

The newly appointed crown prince and deputy crown prince are grandsons of Saudi Arabia's founder, the late King Abdul-Aziz Al Saud, whose sons have passed power from brother to brother since his death in 1953.

The reshuffle comes as the U.S.-allied monarchy faces an array of challenges, including creating millions of jobs for its mostly young population, and amid plunging oil prices that have forced the country to dig into its massive financial reserves. One of the decrees ordered a payment of one month's additional salary to all Saudis working in the security forces, including civilians.

Externally, the Sunni kingdom is locked in a region-wide struggle with Shiite Iran. Riyadh is a leading supporter of the Sunni-led rebellion against Syrian President Bashar Assad, a close ally of Tehran. And for the last month Saudi Arabia has led a coalition that is bombing the Iran-supported rebels in Yemen, known as Houthis.

The kingdom is also increasingly concerned about the threat posed by the extremist Islamic State group, which has repeatedly called for attacks inside Saudi Arabia and the overthrow of the monarchy. On Tuesday, the Interior Ministry announced the arrests of 93 suspected IS sympathizers who were planning attacks on the U.S. Embassy, local security forces and residential compounds housing foreigners. Riyadh is part of the U.S.-led coalition bombing Islamic State militants in Syria and Iraq.

Mustafa Alani, the director of the security and defense department at the Gulf Research Center in Geneva, said Mohammed bin Nayef was likely appointed crown prince because of his counterterrorism expertise, his long experience working with the U.S. and other military allies, and his knowledge of Yemen, where Riyadh is at war with the Houthis and threatened by a powerful local al-Qaida affiliate.

"He is one of the very few in Saudi Arabia who understands Yemen inside out," Alani said.

As interior minister, Mohammed bin Nayef will continue to oversee the country's massive police force and border guards. He will also serve as deputy prime minister.

Alani said the elevation of a new generation to the highest levels of Saudi decision-making — including the supreme economic and security councils put in place by Salman — has led to more pro-active policymaking.

"Decisions are being taken very fast," he said. "They are not hesitating to take the challenge to the Iranian expansionary, interventionist policy."

Salman's appointment of his defense minister son, Mohammed bin Salman, as deputy crown prince deals a "huge blow" to hopes that the conflict in Yemen will end soon, said Jason Tuvey, Mideast economist at Capital Economics.

"Having taken such a bold decision to launch Saudi military involvement in Yemen, it's highly unlikely that Prince Mohammed bin Salman would now want to be seen to be backing down," Tuvey wrote in a report following the announcement.

In another dramatic move, King Salman replaced Foreign Minister Saud al-Faisal -- who has held the position for 40 years -- with Adel al-Jubeir, the ambassador to the U.S., who has been the public face of the Yemen campaign in the West. Al-Jubeir announced the start of the campaign on March 26 during a rare news conference in Washington. He becomes the first non-royal to hold the post of foreign minister.

The 75-year-old Saud al-Faisal spent several months this year receiving medical treatment abroad and the decree cited "health conditions" as the reason for his retirement. He retains the role of royal envoy.

The king also replaced the longtime chairman of the state-owned oil company Aramco, Oil Minister Ali al-Naimi, with Khaled al-Faleh, who was also appointed health minister. Adel Faqih, who had held the labor portfolio, was named economy minister.

The most senior woman in government, Nora al-Fayez, was sacked as deputy education minister for girls. She had earned the wrath of ultraconservatives for pushing to allow physical education for girls in the public school curriculum.

The former crown prince, 69-year-old Muqrin, once headed the kingdom's intelligence agency, but was largely seen as a transitional figure. The royal court statement said he was relieved as crown prince upon his request.

The Allegiance Council, a body made up of the sons and prominent grandsons of the Saudi founder Abdul-Aziz, who vote to pick the king and crown prince from among themselves, voted in favor of Wednesday's appointment of Salman's son as deputy crown prince, the decrees said.

Associated Press writers Adam Schreck in Dubai, United Arab Emirates, and Joseph Krauss in Cairo contributed to this report.