Iraq vowed on Sunday to step up resistance attacks and said more than 4,000 Arabs had come to Iraq ready to "martyr" themselves to defeat a U.S.-led invasion. "The martyrdom attacks by the sons of Iraq and by the armed forces have just begun," military spokesman Hazim al-Rawi told a news conference one day after a resistance bombing at a U.S. checkpoint. "These are the first on the glorious path of Jihad (holy war) against the invaders," he said.

He added that the resistance attack near the central city of Najaf on Saturday had killed 11 U.S. soldiers, rather than four as reported by Washington.

Arabs were also flocking to Baghdad seeking "martyrdom" to defeat the 11-day-old invasion.

"The Mujahideen who have come to Iraq have come from all Arab countries, without exception," he said. "More than 4,000 have already come to Baghdad."

"We are a believing people, a fighting people, Jihad is a must, a duty ordained by God," he said.

Al-Rawi said both the resistance bomber and a man who shot down a U.S. aircraft were called "Ali," a name common among the Shi'ite Muslims who make up more than half of Iraq's population.

He said the participation of Shi'ites, who the United States believes are widely opposed to President Saddam Hussein , showed that Washington faced far greater resistance than expected.

PHOTO CAPTION

A U.S. official said a car exploded at a checkpoint near the Shi'ite Muslim holy city of Najaf, about 100 miles south of Baghdad on March 29, 2003, killing the Iraqi driver and four American soldiers who were searching the vehicle