Saudi Arabia, ever keen to preserve its stability, is likely to act quickly and appoint Prince Nayef bin Abdul Aziz, the obvious choice, as the new heir of the thrown, analysts said.

"There is only one candidate who has all the possibilities of becoming crown prince: Prince Nayef," the interior minister and King Abdullah's half-brother, Abdul Aziz al-Sager, chairman of the Gulf Research Centre, told Agence France Presse.

Saudi Crown Prince Sultan bin Abdul Aziz, whose death was announced on Saturday, was the oil kingpin's defense chief for nearly half a century but was also renowned for his extravagant living and largesse.

A half-brother of King Abdullah, he served as deputy prime minister, and defense and aviation minister from 1962, and was famed among Saudis for his regular, well-publicized acts of largesse, but also for reports that he had benefited massively from government arms purchases.

Saudi Crown Prince Sultan bin Abdul Aziz has died, a palace announcement on state television said on Saturday, throwing his brother Prince Nayef into line to succeed King Abdullah as leader of the key oil producer.

The crown prince, aged around 86, who had served as the kingdom's defense chief for nearly five decades, had been in the United States since mid-June for medical treatment. He was operated on in July but no information had been released on his health since then.

A grand jury in New York has indicted two Iranian men in an alleged plot to get Mexican gangsters to assassinate the Saudi ambassador to Washington, court papers showed Thursday.

The indictment was the next stage in the legal process after the initial complaint against Manssour Arbabsiar, who is in custody, and co-defendant Gholam Shakuri, who is at large.

French President Nicolas Sarkozy on Tuesday voiced deep concern over a U.S.-alleged Iranian plot to kill the Saudi ambassador to Washington and said the West should harden sanctions against Tehran.

"The Americans have given us extremely precise information which shows the credibility of this information and the drift of the Iranian leaders is extremely worrying," he said in an interview to Agence France Presse and French radio stations RCJ and Radio J.

Britain's Treasury said Tuesday it had frozen the assets of five men in connection with the alleged Iranian plot to assassinate Saudi Arabia's ambassador to the United States.

The finance ministry confirmed that it had acted under the Terrorist Asset Freezing Act, after ministers pledged action in response to the purported plan to kill Saudi envoy Adel Al-Jubeir in a bomb attack.

Saudi King Abdullah was hospitalized for a new back surgery in Riyadh, following two similar operations last year in the United States, the SPA news agency early Monday.

The 87-year-old was operated in November for a debilitating herniated disc complicated by a hematoma that put pressure on his spine and underwent another surgery to repair several vertebrae.

Iran is "ready to examine" information the United States says supports accusations Tehran plotted to kill the Saudi ambassador to Washington, Foreign Minister Ali Akbar Salehi said Monday.

"We are ready to examine with deliberation any issue, even if it was fabricated. We have asked America to provide us with information of this scenario," Salehi was quoted as saying by the official IRNA news agency.

Saudi Arabia has asked U.N. chief Ban Ki-moon to inform the Security Council of the "heinous conspiracy" to kill its envoy to Washington, in an alleged Iranian plot, SPA state news agency said on Saturday.

"The Saudi permanent mission to the United Nations in New York has ...formally requested the U.N. secretary general to inform the Security Council of the heinous conspiracy to assassinate the Saudi ambassador," it said.

A top Saudi official warned on Saturday that the kingdom will not tolerate any riots at the annual Muslim pilgrimage to Mecca next month, at a time of rising tension with Iran.

"We will not allow anything that would disrupt the peace of the hajj pilgrimage and disturb the pilgrims. That is why we shall not tolerate any damage, riots or chaos during the season of hajj or out of it," Prince Khaled al-Faisal, governor of Mecca province, told reporters.