RIYADH, Saudi Arabia - King Fahd, whose efforts to strengthen ties between Saudi Arabia - the world's largest oil exporter - and the United States provoked the wrath of Islamic militants, was hospitalized Friday, apparently suffering from pneumonia.

Fahd's half brother, Crown Prince Abdullah, has been Saudi Arabia's de facto ruler since Fahd suffered a debilitating stroke in 1995. Abdullah is expected to become king should Fahd die.

Fahd's hospitalization triggered reports that an emergency had been declared in the kingdom. Officials said on condition of anonymity that an alert had been declared and that military leaves had been canceled or at least discouraged. However, this was firmly denied by the Interior Ministry.

"This is absolutely not true," ministry spokesman Mansour al-Turki said. "There's no canceling of leaves and no state of emergency or anything."

Saudi television station Al-Ekhbariya reported that Abdullah assured Egyptian President Hosni Mubarak during a phone call late Friday that Fahd's health was good and that the medical examinations were going normally.

The official Saudi Press Agency said that Fahd, who is believed to be 82, was admitted to King Faisal Specialist Hospital in Riyadh for unspecified medical tests.

But reports of Fahd's deteriorating health had been blamed for sending the Saudi stock market tumbling 5 percent earlier in the week. Friday's news that he was taken to a hospital helped push crude oil futures to near $52 a barrel ahead of the U.S. Memorial Day holiday weekend, the start of the American summer driving season.

Saudi Arabia's strategic importance as the holder of the world's largest oil reserves and the fact that it is home to Islam's two holiest shrines means even a stable succession could impact world markets and have widespread political fallout.

With the portly, goateed Fahd only a figurehead in the last decade, it has been Abdullah who has overseen the kingdom's crackdown on Islamic militants after followers of Saudi-born Osama bin Laden launched a wave of attacks.