Saudi Arabia's new king moved swiftly Friday to name the country's interior minister as deputy crown prince, making him the second-in-line to the throne, as he promised to continue the policies of his predecessors in a nationally televised speech.

King Salman bin Abdul-Aziz Al Saud's actions came as the oil-rich, Sunni-ruled kingdom began mourning King Abdullah, who died early Friday at the age of 90 after nearly two decades in power, though he officially ascended to the throne in 2005.

Salman's royal decree puts Prince Mohammed bin Nayef in line to ascend to the throne after his designated successor, Crown Prince Muqrin. Mohammed is the son of King Salman's brother Nayef. Like his father, Nayef, who was a formidable power in Saudi Arabia until his death in 2012, Mohammed is head of the powerful Interior Ministry that oversees police and now too holds the title of crown prince.

"We will continue adhering to the correct policies which Saudi Arabia has followed since its establishment," Salman said in the speech aired on the state-run Saudi television station.

Salman on Friday also appointed his son, Prince Mohammed, as Defense Minister. The prince, in his 30s, was head of his father's royal court when Salman was crown prince and is among his most-favored sons.

Salman made an oblique reference to the chaos gripping the greater Middle East as the extremist Islamic State group now holds a third of both Iraq and Syria.

"The Arab and the Islamic nations are in dire need of solidarity and cohesion," the king said.

Salman, 79, had increasingly taken on the duties of the king over the past year as his ailing predecessor and half brother, Abdullah, became more incapacitated.

Abdullah is expected to be buried Friday afternoon following a funeral at the Imam Turki bin Abdullah mosque in the capital, Riyadh.

Leaders from around the world expressed their condolences.

U.S. President Barack Obama described the late Saudi king as a candid leader who had the courage of his convictions, including "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."

The president of the neighboring United Arab Emirates, Sheikh Khalifa bin Zayed Al Nahyan, said in a statement that Abdullah "generously gave a lot to his people and his nation," while Egyptian President Abdel-Fattah el-Sissi said "the Saudi kingdom and the Arab nation have lost a leader of its best sons."

Salman served as defense minister since 2011. That made him the head of the military as Saudi Arabia joined the United States and other Arab countries in carrying out airstrikes in Syria in 2014 against the Islamic State group, the Sunni militant group that the kingdom began to see as a threat to its own stability.

Salman takes the helm at a time when the ultraconservative Muslim kingdom and oil powerhouse is trying to navigate social pressures from a burgeoning youth population -- over half the population of 20 million is under 25 -- seeking jobs and increasingly testing boundaries of speech on the Internet, where criticism of the royal family is rife.

Salman's health has been a question of concern. He suffered at least one stroke that has left him with limited movement on his left arm.