Updated

Saudi Arabia's (search) ruling crown prince warned Islamic militants Tuesday that the kingdom planned shortly to deploy more security forces than they had ever faced before.

"Be assured that the kingdom has enough men whom you haven't seen so far, but within the coming few days you will see them," Crown Prince Abdullah (search) told the militants, whose attacks have increased during the past three months. His remarks were televised.

Westerners in Saudi Arabia are responding to the attacks by moving to high-security compounds or even to Bahrain (search), and by pushing for the right to armed private guards, according to diplomats and real estate agents.

Western embassies in Riyadh (search), the Saudi capital, are negotiating with the government for a relaxation of the ban on private security guards carrying firearms, a Western diplomat said, speaking on condition of anonymity.

Some Westerners have expressed concern that terrorist sympathizers may have infiltrated the Saudi security services, the diplomat said.

Security forces arrested a militant Tuesday north of Riyadh as they stepped up their presence in and around the city in a hunt for the kidnappers of Paul Johnson (search), an American who was abducted Saturday by a group calling itself Al Qaeda (search) in the Arabian Peninsula.

Security officials said the militant was detained in the King Fahd district, but it was not immediately clear whether the detainee was connected to the recent terror attacks.

Johnson, 49, of Stafford Township, N.J., was employed by Lockheed Martin and worked on Apache helicopters.

The day he was seized, Islamic militants shot dead another American, Kenneth Scroggs, from Laconia, N.H., in his garage. Scroggs was the third Westerner killed in a week, after the shooting death of an Irish cameraman for the British Broadcasting Corp. on June 6 and another American who was killed in his garage June 8.

Soldiers with automatic rifles guarded government buildings and manned check points in the city on Tuesday. Other security forces were searching houses where Johnson might be held, a Saudi official said, speaking on a condition of anonymity.

The Interior Ministry set up a hot line to receive information about Johnson or possible terrorist attacks.

In his appearance on television, the crown prince addressed a group of writers, intellectuals and clerics, urging them to take a proactive position against Islamic militancy.

"What is required from you as brothers, as clerics, as writers, is not to be silent," Abdullah said. "Silence is a crime against your religion, against your country and against your people."

The U.S. Embassy in Riyadh has advised Americans to leave Saudi Arabia, and Britain has authorized the voluntary departure of its nonessential embassy staff and their families.

"There is no overcrowding at consulates and there is no panic among Westerners to leave," a Western diplomat said, speaking on condition of anonymity.

An estimated 35,000 Americans have been working in Saudi Arabia. It was not clear how many have left since the terror attacks became more frequent in April. Western diplomats said Monday that Americans and others were leaving in response to the violence, but that it could not be described as an exodus.

A real estate agent in Riyadh told The Associated Press that Westerners were moving from parts of the capital seen as less secure to walled compounds and upscale neighborhoods with greater security.

"They will feel safer as more security forces are deployed [in those areas]," the real estate agent said, speaking on a condition of anonymity.

Foreigners who work in the oil industry, and live on the eastern coast of Saudi Arabia, have even crossed international borders to sleep soundly.

"Foreigners working in the oil industry have been renting houses in neighboring Bahrain," a second real estate agent told the AP. "They finish their work and come back the next day."

Bahrain is just a 30-minute drive across the 18-mile King Fahd Causeway from eastern Saudi Arabia.