(CNN) -- Funeral services were held Sunday for Saudi Crown Prince Nayef bin Abdulaziz, a hard-line conservative credited with pushing back al Qaeda.
Nayef, named crown prince in October by his brother the king, was heir to the Saudi throne. Saudi state TV, which reported his death Saturday, broadcast Quran readings as an expression of mourning for the prince, who died in Geneva, Switzerland. He was in his late 70s.
"It is a shock. We all knew his health was frail, but his death is a shock," Saudi Foreign Ministry spokesman Osama Nogali said. "We still don't know the reason behind his death."
The Saudi Press Agency published a statement from the Royal Court, saying it "condoles the Saudi people on the deceased prince pray to God to bless his soul and to reward him for his services to his religion and homeland."
Nayef's body arrived at the Grand Mosque in Mecca on Sunday. He was to be buried following the funeral in Al-Adel cemetery in Mecca, according to Oussama Nogali, Saudi foreign ministry spokesman.
Saudi King Abdullah was in attendance at the funeral, along with Gen. Hussein Tantawi, head of Egypt's Supreme Council of the Armed Forces.
After the funeral, a period of mourning -- most likely for three days -- will be announced, a Saudi official said. The official asked not to be named because he is not authorized to speak to the media.
U.S. President Barack Obama released a statement Saturday offering his condolences.
"Under his leadership, the United States and Saudi Arabia developed a strong and effective partnership in the fight against terrorism, one that has saved countless American and Saudi lives," Obama said.
He praised Nayef for supporting a broad partnership between Saudi Arabia and the United States.
U.S. Vice President Joe Biden similarly offered his condolences, and hailed the former leader as an important ally in the fight against terror.
It is expected that authorities selected by the king to choose a successor will meet as soon as the mourning period is over, the official said. A new crown prince could be named within the next three to four days, the source said.
Nayef served as Saudi interior minister since 1975, overseeing the kingdom's counterterrorism efforts.
He also served as deputy premier.
A classified U.S. Embassy cable leaked by the website WikiLeaks described Nayef as a hard-line conservative who was lukewarm to King Abdullah's reform initiatives.
Nayef led the crackdown against hard-line Islamists who took control of Mecca in 1979 and also oversaw the smashing of Saudi-based al Qaeda cells in the mid-2000s.
In recent years, his son, Prince Mohammed bin Nayef, has led the kingdom's fight against al Qaeda as the elder Nayef seemed to have taken more of backseat.
On Saturday, the Bahrain state-run news agency announced three days of mourning in that country and ordered flags to be lowered to half-staff there and at its embassies abroad. Kuwait also announced a three-day mourning period.
CNN's Rima Maktabi, Hamdi Alkhshali, Mohammed Jamjoom and Kevin Flower contributed to this report.