With security on high alert and extra troops deployed near the U.S. Embassy and other sensitive sites, thousands of demonstrators began gathering at cities across the country on Friday to protest a potential U.S.-led war against Iraq.

About 7,000 people gathered outside the Madni Masjid mosque in the Western city of Peshawar, chanting "Down with America," and "Long Live Saddam Hussein." Many more were expected as the demonstrations gained momentum during the day.

In the capital, Islamabad, about 400 people rallied out the Red Mosque, some carrying banners that read "American Terrorism," "Yankees: Don't Spread Hatred in the Muslim World" and "Stop the Holocaust Against Muslims."

Several dozen police stood nearby wielding anti-riot shields and sticks; traffic was diverted and two fire trucks were parked at the edge of the crowd, but crowd remained mostly calm and there was no violence.

"The U.S. has started a war against Muslims," cleric Samiul Haq told the protesters from a small platform outside the mosque. "This is a war between the friends of Allah and the friends of Satan."

The demonstrations -- called by hard-line Islamic leaders that won unprecedented support in recent nationwide elections -- were took place in all of Pakistan's major cities.

The religious leaders also called for shops to shutter their windows in allegiance, but it appeared that many were staying open. Most shops in Peshawar were open, despite the strike. In the eastern city of Lahore, some shop owners said they were staying shut for fear of violence.

Supporters say the marches are just a taste of the anger that an attack on Saddam Hussein's regime would cause in Pakistan, a deeply conservative Muslim country but a crucial ally in the U.S.-led war on terror.

"The American attack on Iraq will be an attack on the Islamic world," said Fazl-ur Rahman, a one-time candidate for prime minister and a leader of the Islamist coalition, called the Mutahida Majlis-e-Amal. "If today we cannot stop America from attacking Iraq, then tomorrow they will attack Iran, and then it could be Pakistan."

There have been a series of terrorist attacks on Westerners and Pakistani Christians since President Gen. Pervez Musharraf's decision to side with the United States in its efforts to topple the Taliban regime in neighboring Afghanistan, and some fear the anger will intensify if America wages war on another Muslim country.

The U.S. Embassy said it was monitoring events, but not unduly concerned.

"We're watching events closely," said spokesman Terry White. "But it's not accurate to say we're behind-the-barricades afraid. ... We've been security conscious for months."

Most Western embassies in Pakistan are already operating at emergency levels, with families evacuated after a grenade attack on a church in March that killed a U.S. Embassy employee and her 17-year-old daughter. In June, a car bomb went off outside the U.S. Consulate in Karachi, killing 12 Pakistanis. A suicide bombing in that southern city in May killed 14 people, including 11 French engineers.

Interior Ministry spokesman Iftikhar Ahmad said extra police will be deployed outside the U.S. Embassy in Islamabad and consulates in other cities during Friday's marches.

"Sentiments are always high when clerics hold rallies against America, but the provincial governments have prepared security plans to maintain law and order," he said.

Pakistan's government, which on Jan. 1 took over a seat on the U.N. Security Council, has been reluctant to discuss it's position on Iraq. But Prime Minister Zafarullah Khan Jamali urged his countrymen not to waste their energy defending Saddam Hussein's regime.

"Give a glance back in history, and see whether Iraq helped Pakistan during its times of crisis," Jamali said last week.

Protests got under way in the afternoon, after traditional Friday prayers in which hard-line clerics rallied their supporters at mosques.

Religious leaders promised that their supporters would not resort to violence.

"We will be peaceful," said Qazi Hussain Ahmad, the leader of Pakistan's oldest and most organized religious party, Jamaat-e-Islami, which is a member of the coalition.

Even before Friday's protests got underway, tensions were heightened after a weekend shootout between American and Pakistani forces along the Pakistan-Afghan border. A U.S. warplane dropped a bomb along the border after a rogue Pakistani border guard shot and wounded an American soldier.

The U.S. military says the entire clash took place on Afghan soil, but Pakistan's government says only that it is investigating to see if the Americans crossed over into its territory.