(CBS/AP) Police killed two militants during a shootout at a fortified hideout in the holy city of Mecca on Monday and seized a large cache of weapons, according to a Saudi Interior Ministry official.

Police foiled a terrorist operation "that did not respect the sanctity of holy places and the month of Ramadan" — the holy month of fasting that began days ago, the official told The Associated Press on condition of anonymity.

The official said that in light of the shootout, Saudi police will increase security in Mecca, particularly during the last 10 days of Ramadan, when some 2 million Muslims are expected to perform the "omra," or minor pilgrimage, to the city — the birthplace of Islam's seventh-century prophet.

The shootout started after police surrounded two premises that the militants had fortified and ringed with sandbags in Mecca's al-Share'a neighborhood at 8 a.m. local time (midnight ET), the official said. Police had been monitoring the premises for the previous 24 hours.

"The terrorists began shooting heavily at security forces, using automatic rifles and hand grenades," the official said.

While a security forces helicopter hovered overhead, police fired back at the militants as they were attempting to flee the area in two cars, hitting one of the vehicles and killing two of its occupants.

A cache of weapons and bombs were found inside the car, the official said.

Security also seized firearms including Kalashnikov rifles, hand grenades, rocket-propelled grenades and material to make explosives in the raided premise. Passports, identification cards and thousands of flyers bearing the picture of al Qaeda terror chief, Saudi dissident Osama bin Laden, were also found.

Police are searching for the militants who escaped, the official said. It was not clear how many were at large.

Saudi Arabia has been under pressure to crush networks that include al Qaeda, the terror group blamed for the Sept. 11, 2001 attacks on the United States. Fifteen of the 19 Sept. 11 hijackers were Saudis.

Saudi officials have been irked by continued allegations by U.S. officials of links between the kingdom and terror groups. Last year, it emerged that payments from the wife of Saudi ambassador to the United States made their way to two of the hijackers.

To polish their negative image, Saudi Arabia has spent $17.6 million on public relations, advertising and lobbying since the Sept. 11 attacks

The government has also been cracking down on Islamic militants since May 12 suicide bombings in Riyadh killed 26 people and nine attackers.

On June 14, a raid on a terror cell plotting attacks in Mecca killed five al Qaeda militants and two security agents. Police also found six dozen bombs and other weapons in the militants' hideout.

More than 200 suspects have been arrested and more than a dozen killed in a series of high-profile police raids since the Riyadh attacks.

The Riyadh bombings also sparked unprecedented public discussion of the role of religion in Saudi society, with some daring to argue that the strict form of Islam preached in the kingdom fostered intolerance and extremism.

Saudis had reacted angrily to the threats against Mecca — the holiest place in Islam and the heart of the annual pilgrimage every able-bodied Muslim is required to perform at least once.

The legitimacy of Saudi rulers rests partly on their custodianship of Mecca, which is off-limits to non-Muslims. A strike on Mecca could be seen as a strike on the regime.

Last week, a U.S. advisory warned Americans living in Saudi Arabia to be "particularly vigilant" for terrorist attacks during the holy fasting month.

The U.S. also warned it has credible intelligence of a terrorist threat to commercial aircraft.

The State Department advisory suggests Americans "defer non-essential travel to Saudi Arabia."

"The U.S. government continues to receive indications of terrorist threats aimed at American and Western interests, including the targeting of transportation and civil aviation," the department said in a statement.

"There is credible information that terrorists have targeted Western aviation interests in Saudi Arabia," the warning continued. "American citizens in Saudi Arabia should remain vigilant, particularly in public places."