(CNN) Throngs of mourners gathered in Mecca early Friday just hours after Saudi Arabia's King Abdullah bin Abdulaziz al Saud died. He was 90.

Prince Salman bin Abdulaziz was appointed as the new king, state television reported.​

The announcement of Abdullah's death comes several weeks after the state-run Saudi Press Agency said he was suffering from pneumonia and had been admitted to the hospital

Services will be held Friday afternoon at the Imam Turki Bin Abdullah Grand Mosque in Riyadh, and many world leaders are likely to pay their respects.

Jordan's King Abdullah cut short his visit to Davos, and is heading to Riyadh, according to a Jordanian government source.

"King Abdullah's life spanned from before the birth of modern Saudi Arabia through its emergence as a critical force within the global economy and a leader among Arab and Islamic nations," U.S. President Barack Obama said in a statement.

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He praised Abdullah's role in sponsoring the Arab Peace Initiative, which attempts to solve the long-simmering conflict between Israel and Palestine.

"This is a sad day. The United States has lost a friend, and the Kingdom of Saudi Arabia, the Middle East, and the world has lost a revered leader," U.S. Secretary of State John Kerry said in a statement. "He was so proud of the Kingdom's journey, a brave partner in fighting violent extremism who proved just as important as a proponent of peace."

A cautious reformer

King Abdullah became king of the oil-rich nation, a key U.S. ally in the Middle East, in August 2005. But he had been running Saudi Arabia since 1996, after his half-brother King Fahd's stroke.

In the context of the kingdom's conservative circles, Abdullah was seen as reformer and often came up against the more hard-line clerics.

Photos: Monarchies around the world Photos: Monarchies around the world King Salman bin Abdulaziz al Saud succeeded one of his brothers, King Abdullah, on the throne of Saudi Arabia in January 2015. Hide Caption 1 of 32 Photos: Monarchies around the world King Maha Vajiralongkorn Bodindradebayavarangkun assumed the throne in Thailand in December 2016, nearly two months after the death of his father, King Bhumibol Adulyadej Hide Caption 2 of 32 Photos: Monarchies around the world Hamad bin Isa Al Khalifa, shown here in November, is King of Bahrain. Hide Caption 3 of 32 Photos: Monarchies around the world Bhutan's King Jigme Khesar Namgyel Wangchuck, shown here with his wife, Queen Jetsun Pema, is known as the "Dragon King." He became king of the South Asian country after his father abdicated in 2006. Hide Caption 4 of 32 Photos: Monarchies around the world Britain's Prince Philip, Duke of Edinburgh, and Queen Elizabeth II have been married since 1947. 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Since ascending to the throne, Abdullah took steps toward broader freedoms and invested some of the country's vast oil wealth in large-scale education and infrastructure projects.

"He was really quite (an) extraordinary figure. He was probably the most progressive and liberal minded king of Saudi Arabia since King Faisal, which is a long time ago, in the early 1970s," CNN's Fareed Zakaria said about Abdullah, who he described as "much loved."

"I had the opportunity to meet with him once and what you got a sense of was somebody who really was determined to move his country forward," Zakaria said. "It's a conservative country and a conservative society -- and he kept emphasizing that to me -- but he was very clear in the direction he wanted to go."

However, resistance from conservative factions hindered some of his efforts, leaving many women in particular disappointed by a lack of progress toward greater independence.

What's next?

Under Abdullah's leadership, the country slowly squashed al Qaeda, capturing or killing its leaders in the kingdom, forcing the remnants underground and sidelining radical preachers.

It also took a more prominent role in international affairs.

Last year, it became the lead Arab nation in a U.S.-led coalition to eradicate the ultraradical ISIS group in Iraq and Syria.

Photos: Saudi Arabia's King Abdullah Photos: Saudi Arabia's King Abdullah Saudi Arabia's King Abdullah – Saudi Arabia's King Abdullah bin Abdulaziz al Saud speaks at his private residence in Jeddah, Saudi Arabia, in June. The King has died, according to an announcement on Saudi state TV. He was 90. Hide Caption 1 of 11 Photos: Saudi Arabia's King Abdullah U.S. President Gerald Ford accepts a gift from Prince Abdullah in Washington in July 1976. Abdullah became King of the oil-rich nation, a key U.S. ally in the Middle East, in August 2005. Hide Caption 2 of 11 Photos: Saudi Arabia's King Abdullah Seated from left, Prince Abdullah, U.S. Secretary of State Jim Baker, U.S. President George H.W. Bush and Saudi King Fahd discuss the Gulf crisis in November 1990. Hide Caption 3 of 11 Photos: Saudi Arabia's King Abdullah Iranian President Mohammad Khatami meets Prince Abdullah in December 1997, during a break of the Islamic Conference summit in Tehran, Iran. Abdullah was the highest-ranking Saudi official to visit Tehran since the 1979 Iranian Islamic Revolution. Hide Caption 4 of 11 Photos: Saudi Arabia's King Abdullah Britain's Queen Elizabeth and Prince Philip meet with Prince Abdullah for lunch at her Scottish residence, Balmoral Castle, in September 1998. Hide Caption 5 of 11 Photos: Saudi Arabia's King Abdullah Venezuelan President Hugo Chavez hugs Prince Abdullah during a summit in Caracas, Venezuela, in September 2000. Hide Caption 6 of 11 Photos: Saudi Arabia's King Abdullah From left, Jordan King Abdullah II, Saudi Prince Abdullah, U.S. President George W. Bush, Egyptian President Hosni Mubarak, Bahrain King Hamad bin Isa Al Khalifa and Palestinian Prime Minister Mahmoud Abbas stand together for a group photo after meeting in Sharm El-Sheikh, Egypt, in June 2003. Hide Caption 7 of 11 Photos: Saudi Arabia's King Abdullah King Abdullah is surrounded by hundreds of Islamic clerics, tribal chiefs and other prominent Saudis before a ceremony bestowing his legitimacy in August 2005. Hide Caption 8 of 11 Photos: Saudi Arabia's King Abdullah The King poses with U.S. President George W. Bush during an economic summit in Washington in November 2008. Hide Caption 9 of 11 Photos: Saudi Arabia's King Abdullah King Abdullah is escorted by Turkish President Abdullah Gul as Lebanese Prime Minister Najib Mikati, left, walks alongside them during a summit in Mecca, Saudi Arabia, in August 2012. Hide Caption 10 of 11 Photos: Saudi Arabia's King Abdullah The King meets with U.S. President Barack Obama at Rawdat Khurayim, the monarch's desert camp in Saudi Arabia, on March 28. Hide Caption 11 of 11

Analysts are predicting a smooth political transition despite the many challenges facing Saudi Arabia, including Iran, the rise of ISIS, the crisis in Yemen, and the drop in oil prices.

Saudi Arabia has 16% of the world's known oil reserves, according to the U.S. Energy Information Administration. The country is widely seen as the leader of OPEC and has a large influence on energy prices and political stability in the Middle East.

"Remember, the last time the price of oil fell like this, the Soviet Union collapsed," said Zakaria. "That said, the successor is a very competent man."

He added: "I don't expect any major shift, but it marks a big change, and we'll have to see what the new king is like."