WASHINGTON (AP) _ Saudi security forces probably fired shots at rioters in Mecca on July 31, a U.S. official said Tuesday, contradicting Saudi statements that none of the 402 victims was killed by guns.

''It seems like there were some shots fired'' in response to ''extreme violence'' by Iranians visiting the holy city for the annual Moslem pilgrimage, said the official, speaking on condition of anonymity.

The official's comments, based on information received since the deadly riots at Mecca, jibe with eyewitness accounts of non-Iranian Moslems who said they saw Iranian pilgrims shot, trampled and beaten to death by Saudi law enforcement officers.

The Iranian government claimed the death toll was high because Saudi police used machine guns. But Saudi officials, including Prince Bandar Bin Sultan, the Saudi ambassador to the United States, said ''not a single bullet was fired.''

Deaths and injuries were caused by trampling of people in the crush of the riots, the Saudis said. They said the 402 people killed at Mecca included 275 Iranians, 42 other pilgrims and 85 policemen.

The U.S. government official said the Saudis apparently were provoked into firing shots after at least one security officer was killed. He said the Iranians were armed with knives and other objects.

The United States says the Iranians instigated the riots, and the Saudis handled the disturbance responsibly.

After the riots, Washington had no evidence to believe that shots had been fired by the Saudis, but new evidence has come to light in the past month, the official said.

Several pilgrims have said they saw shots fired by the Saudis. Suleiman Masawra, 51, of Kfar Kara in northern Israel told reporters last month that after the violence began, the Iranians attacked cars. ''Then the shots started. I saw the Saudi police attacking them,'' he said.

Masawra said he saw some Saudi police run because they were unarmed, but mobs of uniformed Saudis joined the fray.

The conflict between Iran and Saudi Arabia stems in part from the division between the Shiites and Sunni sects of Islam. About 85 percent of the world's Moslems are Sunnis, but most Iranians are Shiites.

Iran's leader, the Ayatollah Ruhollah Khomeini said after the riots that the Saudi leaders, who are Sunnis, were unfit to serve as guardians of Islam's holy sites.