RIYADH: Saudi Arabia buried King Abdullah Friday as foreign leaders gathered in the capital for the funeral of the ruler of the world's top oil exporter and the spiritual home of Islam.

Abdullah, a cautious reformer who led his kingdom through a turbulent decade in a region shaken by the Arab Spring uprisings and extremism, died early Friday aged about 90.

He was replaced by his half-brother Salman, who moved quickly to consolidate his hold on power and vowed to maintain a steady course for the kingdom.

Salman joined Gulf rulers and leaders including Turkish President Recep Tayyip Erdogan and Prime Minister Nawaz Sharif for a funeral service at Riyadh's Imam Turki bin Abdullah mosque.

Abdullah's shrouded body was borne on a simple litter by members of the royal family wearing traditional red-and-white checked shemagh head gear.

The body was quickly moved to nearby al-Od public cemetery where it was buried.

Citizens were invited to pledge allegiance to Salman at the royal palace. Another of the late monarch's half-brothers, Moqren, was named crown prince.

In his first public statement as the new ruler, 79-year-old King Salman vowed to “remain, with God's strength, attached to the straight path that this state has walked since its establishment”.

He called in televised remarks for “unity and solidarity” among Muslims and vowed to work in “the defence of the causes of our nation”.

Moving quickly to clear uncertainty over the transition to the next generation, Salman named the interior minister, Prince Mohammed bin Nayef, as second in line to the throne.

He also appointed one of his own sons, Prince Mohammad, as defence minister.

Officials did not disclose the cause of Abdullah's death, but the late king had been hospitalised in December suffering from pneumonia and had been breathing with the aid of a tube.

Obama hails ‘valued’ ally

Under Abdullah, who took the throne in 2005, Saudi Arabia has been a key ally of Washington in the Arab world, most recently joining the US-led coalition carrying out air strikes against the Islamic State group in Syria and Iraq.

President Barack Obama was quick to pay tribute to Abdullah as a “valued” ally.

“The closeness and strength of the partnership between our two countries is part of King Abdullah's legacy,” Obama said in a statement shortly after the monarch's death.

Vice President Joe Biden said on Twitter he would lead a delegation to Saudi Arabia “to pay respect and offer condolences”.

Other tributes came in from foreign leaders, with French President Francois Hollande hailing Abdullah as “a statesman whose work profoundly marked the history of his country”.

British Prime Minister David Cameron said he was “deeply saddened” and that Abdullah would be remembered for “his commitment to peace and for strengthening understanding between faiths”.

As the top producer in the Organisation of Petroleum Exporting Countries, Saudi Arabia has been the driving force behind the cartel's refusal to slash output to support oil prices, which have fallen by more than 50 per cent since June.

But prices surged Friday, amid uncertainty over whether the new king would maintain that policy. The International Energy Agency's chief economist said he did not foresee major policy shifts.

“I do not expect any significant change in the oil policy of Saudi Arabia and I expect and hope that they will continue to be a stabilisation factor in the oil markets,” Fatih Birol said in Davos, Switzerland.

Royal family stalwart

Saudi Arabia is home to Islam's holiest sites, Makkah and Madinah, and its role as a spiritual leader for Sunni Muslims has seen it vying for influence with Shia-dominated Iran.

Tehran nonetheless offered its condolences, saying Foreign Minister Mohammad Javad Zarif would travel to Riyadh to take part in official ceremonies on Saturday.

Behind his thick, jet-black moustache and goatee, Abdullah had a shrewd grasp of regional politics.

Wary of the rising influence of Islamist movements, Saudi Arabia has been a generous supporter of Egyptian leader Abdel Fattah al-Sisi since the army's ouster of Mohamad Morsi of the Muslim Brotherhood.

Egypt declared seven days of official mourning for Abdullah.

Saudi Arabia has also played a key role in supporting opposition to Iran-backed President Bashar al-Assad of Syria, allowing US troops to use its territory to train rebel fighters.

Salman is widely expected to follow closely in Abdullah's footsteps, in foreign and energy policy as well as in making moderate reforms to the 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 Organization, tapping into the country's massive oil wealth to build new cities, universities and high-speed railways.

‘Insensitive to human rights’

But Saudi Arabia is still strongly criticised for a dismal human rights record, including the imprisonment of dissidents. It is also the only country in the world that does not allow women to drive.

“The Saudi regime seems insensitive to human rights and human dignity and unfortunately they are also protected by many Western countries because they have oil and because they are seen as allies in the fight against terrorism,” Amnesty International head Salil Shetty said in Davos.

Salman is a stalwart of the royal family credited with transforming Riyadh from a backwater to a thriving capital during his half-century as governor.

Since the death in 1952 of the kingdom's founder, King Abdul Aziz bin Saud, the throne has passed systematically from one of his sons to another.

Abdul Aziz had 45 sons. Abdullah, Salman and Moqren were all born to different mothers.

Saudi Arabia has managed to avoid the social upheaval that has shaken many of its neighbours in recent years, thanks in large part to massive public spending.

But the new king will face some major challenges, especially as falling oil prices cut into state revenues.