TEHRAN -- The main Iraqi Shia opposition group on Friday vowed that Shias in Baghdad would stay out of the conflict, as U.S. troops were closing in on the Iraqi capital.

"They will try to remain on the sidelines to suffer the least possible damage, until they are certain that the Iraqi regime's repressive machine has been annihilated," an official from the Supreme Assembly of the Islamic Revolution in Iraq (SAIRI) told AFP.

"When this point is reached, they will start organizing themselves," Mohsen Hakim said.

Troops of the U.S.-British coalition were nearing Baghdad Friday and controlled much of Saddam International Airport, 20 kilometers (12 miles) from the city center.

The Pentagon is betting on the collaboration of the Shia half of the population in the five-million-strong capital, persecuted by the regime of Saddam Hussein.

"Given Shias are half the population ... you probably have people ready to help out, you have to be patient," Chairman of the Joint Chiefs of Staff General Richard Myers said.

Saddam and most of his regime are from Iraq's Sunni minority.

At the beginning of the war two weeks ago, SAIRI Chief Mohammad Baqer Hakim urged Shias to remain neutral, blaming both the Americans and Saddam for the war.

The coalition has decided not to include the Shias in its war effort, unlike the Kurds in the north who are advancing on government-controlled cities backed by U.S. and British aircraft.

However in Beirut, Sheikh Hussein Fadlallah, spiritual leader of Lebanon's fundamentalist Shias, called on all Muslims to resist the coalition forces in their drive to Baghdad.

"We urge U.S.-British forces not to attack holy sites (in Najaf and Karbala) and we call on Muslims and free men around the world to resist the invaders," he told worshipers after Friday prayers in Beirut.

"The enemy plans to reduce the umma (the Muslim nation) to impotence to impose on it new regimes serving them and replace a dictator (Saddam) by a tyrant of their own," Sheikh Fadlallah warned. On Friday, Saddam was quoted by his Information Minister, Mohammad Said al-Sahhaf, as calling on all Baghdadis to resist advancing U.S.-British forces, saying, "We believe in God and we count on Him for a victory which he has promised to believers, and that is our right."

The central Iraqi cities of Najaf and Karbala, which have been the scene of intense fighting between coalition troops and Iraqi forces, are the holiest in Shiite Islam after Mecca and Medina.

The Shiite religious leader in Najaf, Ayatollah Mirza Ali Sistani, had denied a U.S. military report that he had issued a fatwa (religious decree) calling on the populace not to impede coalition military forces, Arab news channel Al-Jazeera reported Friday. On the contrary, Iraqi television said Sistani and four other top Shia clerics at Najaf had called on Iraqis of all beliefs and ethnic groups to unite in the defense of their country against "the enemies of God and humanity."

The television showed an aged cleric, who was not identified, reading the fatwa to this effect.